Classically, in the Northern hemisphere , a " touring" bike will be made with relatively expensive, strong but light weight tubing .It will be very stable in its handling and comfortable to ride for long periods, with relaxed, shock absorbing geometry and a leather saddle. It's likely to have narrow, low resistance tyres, narrow drop bars and a high top bar, brazed-on rack mounts, preferably mountings for three bottles , double eyelets front and rear, proper mudguards , and a dynamo lighting system. It will be fast - over good roads, anyway - but uncomfortable or impossible over the rough for extended periods. Such bikes are most practical on the well paved roads of in Europe or North America , where high population densities provide the infrastructure of well sealed roads and established hospitality services. In those environments, touring by bike is feasible with very little luggage ( "credit card touring" in the USA , or what the British call "hostelling tours") and for that purpose the classic touring bike is fine. However, it might be more useful to think of these bikes, especially with their 700C wheels, as light tourers.
What the touring bike lacks is "rough road" capability, and perhaps the capacity easily to carry the extra amount of luggage - tent, sleeping bag, food, cooking equipment, and especially water - required for a fully self supported bicycle camping tour, away from hostels and restaurants.
In Australia, the variability of road surfaces and the relatively sparse availability of services, as well as a harsher summer climate, mean that the touring bike of the Northern hemisphere is less than fully practical. Here, unless we are prepared to stay on busy highways - or spend a lot of time in a SAG bus - we need to be able to cope with at least some rough roads, a lack of readily available services, and the need to carry camping gear and supplies , especially water. Independent long distance touring in Australia is simply not possible if one is dependent on hotels and restaurants. (Increasingly, though , "supported" tours are becoming fashionable, where you pay someone else - usually in a truck - to do the hard part of carrying any equipment you need. You have to be able and willing to pay the bill for that level of service.)
In view of these problems, many Australian cyclists turn to the MTB for independent bicycle travel in our country. So......
Why not a Mountain Bike?
The MTB evolved in the 1980's, essentially as a robust off road machine for semi competitive day rides, in the reliably mild weather of California - racing capability was a greater consideration than load carrying capacity; and even today many MTB's have neither racks nor fittings to mount them. The MTB is intended to be an off road bike for relatively short journeys, (probably with a car at each end) - it needs no mudguards, no dynamo lights, little carrying capacity ; in fact, these long distance essentials would get in the way of its intended purpose.
The MTB also has the high bottom bracket that enables a skilled rider to perform spectacular tricks, take corners fast and fly down rocky descents at great speed. That high bottom bracket also means it has very positive, twitchy steering , especially when combined with a short wheel base. These characteristics allow a fast rider (who has the required motivation and concentration ) to ride very quickly through terrain that would be impossible on a TB at the same speed. The current popularity of suspension is for the same purpose, really designed to cater for the very restricted ( and ecologically damaging ) activity of " downhilling". Even though most MTB buyers will never want to do these quite dangerous racing stunts and tricks, retail advertising heavily promotes them and bike shops use them as sales levers to "wannabe’s" who admire those tricks and wish to copy them.
Unfortunately, many other impressionable bike buyers, especially less energetic ones, are oversold by contemporary sales techniques, and surprisingly ignorant bicycle journalism in several countries. For such potential buyers, including the expeditioner, the MTB’s geometry and characteristics are a poor choice.
In terms of componentry too, the modern MTB has little to offer the independent cycle expeditioner, as gear and brake elements become increasingly "disposable", for the sake of quick replacement in racing events where saving time is more important than long term serviceability.
So, while the MTB is well suited to off road bicycle racing, (a limited , short term activity which is fixed in space and time), such a bike is less than ideal for the open-ended nature of extended bicycle touring .
While many recreational cyclists will say they are happy enough with one bike, usually an MTB or "hybrid", many of them will also refuse to ride off sealed roads. This reinforces the observation that it is not possible to have an all-purpose bike - some compromises are necessary in your cycling activity, unless you have several bikes, eg racing/ commuting/ touring/ MTB-ing. It depends how many compromises you are prepared to make. Do you really need the characteristics of ALL the different types of bikes ? Think about what you're going to do, and how often you're going to do it - many people will never want to race, so why have a semi-racing bike ? Other people would never go camping, so why have the capacity for the various extra items that are necessary for camping ?
If however you want a bike to carry you independently more or less anywhere across a range of surfaces, especially for long distances, over an extended period, you may need to consider a "camping" bike. Not least, such a bike makes choosing a route that much easier, as you can simply go where you want to go without worrying too much about surfaces, and also know you can carry supplies and equipment, independently of other support.
As long as you are not interested in winning races, it’s possible to come up with a much better concept than either the (light) tourer or the MTB as an ideal Australian bike. So the choice is not only between a " touring " bike and an MTB. It is - or would be - possible to combine the best elements of both. But , in the face of the concerted hyping of the international bicycle industry, there is little demand for a camping bike which is for the moment a niche market that is almost totally ignored.
What would a "camping bike" be like ?
steel frame (repairable), as strong as an MTB , but not so heavy.
long wheel base, for heel/pannier clearance, and stability over rough ground
low bottom bracket (for stability, and easy stand over clearance, especially when loaded)
capacity for heavy loads (eg water + food) without excessive frame flex
all braze-on's : four point rack fixings and double eyelets, front and rear etc. Several bottle bosses, dynamo bracket, spoke holders etc
leather saddle, comfortable over long periods, good "sight seeing" riding position
durable, heavy duty wheels ( don't break spokes)
wide tyres , ( for grip and puncture resistance, "go anywhere" capability )
good clearance for mudguards ( bike stays cleaner, clothes and luggage better protected from road grime)
integrated light system, for long term, self sufficient reliability. Storage dynamo lights.
user-serviceable components ( hubs, BB etc) rather than throw away cartridges
friction gear shifters, for serviceability
http://users.chariot.net.au/~gloria/backroad.html
