If you want a bike for extended touring carrying camping gear, then check out a prime example, the Bruce Gordon BLT. This is setup as most experienced tourists would choose. The standard "production" touring bike, the Trek 520, needs a makeover before it is tour-worthy.
For hostel style touring, where you dont carry camping gear, then you can ride something lighter and faster. You still need fittings for rack, fenders, etc, and clearance for decent sized tyres, but you can use long caliper brakes rather than MTB style cantelevers.
Racing style road bikes are suitable for weekend trips , supported touring and ultra-light hostel touring, but you will have difficulty carrying luggage for extended trips.
Most touring bikes (except Canondale) are made in steel because steel is easy to build in small workshops. It is also durable, comfortable and easy to repair, should you have a quality bike repair shop to hand.
A carbon bike may survive a long tour, but the material has not really been proven in touring bikes. Specialised do make the Sequoia, which is a fairly good light-tourer.