If you're buying a bike for touring and nothing else, then by all means get a touring bike. If the bike will primarily be for touring and some other occasional riding, then also get a touring bike. But if this is to be your one and only all-purpose bike, then you might need to think harder.
A touring bike to the untrained eye looks just like an ordinary road bike, but it has many, many advantages for touring. Here's my list of what you would want if you could have everything. You don't need everything of course, but if you're buying a bike just for touring, then why not?
1. Many touring bikes are steel, but some are aluminum. I would buy steel, but I wouldn't consider aluminum to be a show-stopper.
2. Widely spaced fork and rear triangle allow for the wider tires you need to handle a variety of surfaces and produce a more comfortable ride.
3. Low gearing, often using mountain bike rather than road bike gears and derailleurs, is good for getting a loaded bike up the 100th hill of the day.
4. Fittings for as many water-bottle cages as you can get (at least three), unless you plan to use a Camelback (not very common among road cyclists).
5. Front fork fittings for a front rack.
6. Seat-stay fittings for a rear rack.
7. Long chain stays to move the panniers back far enough to avoid heel strike without putting the weight behind the rear hub.
8. Strong wheels to avoid spoke breakage under heavy loads. 36 3-cross spokes is pretty standard.
9. Long wheel base for a stable and comfortable ride.
10. Drop handlebars for a variety of hand positions.
11. Fenders for riding in the rain.
If you buy a bike described by the manufacturer as a touring bike, you will get many if not all of the things in my list above. Most major manufacturers make one or two touring bikes. The Surly Long Haul Trucker and the Trek 520 are two popular models, but there are many other fine choices. Be sure to read:http://www.adventurecycling.org/features/buyersguide.cfm
Note that most bike shops do not keep touring bikes on the floor. So you may need to buy one sight-unseen. And you may need to wait months to get it, so act early.