Unlike the other posters on this thread, I've never been on a bike tour and just two weeks ago my Trek 520 was still in the LBS. I am a newbie still in the process of getting all the "stuff."
Unlike many other newbies, I know how to get by for a week with just 15-20 pounds of stuff. While there will be a few more bike specific things, I already have most of it. Learning what's needed and not takes time, and varies from person to person. It can't just be read in a book or on the internet.
As for the bike, I know that a bike like the Trek is not really needed for a week long tour. I have a job with limited vacation time, so it won't be going across the country or other muilti-week trips. However, that isn't the main reason I got my bike.
Touring bikes are excellent general purpose bikes. They are perfect for commuting and running errands on. The Trek will be partly replacing my current bike, a sport touring Centurion from the 70's that I got off Craigslist. While the Centurion is still a good bike, it not in good enough shape for a week long tour.
Perhaps other touring newbies recognize the many possible uses for a touring bike. They are well designed, and properly maintained, can last decades.
Getting all the stuff first, then the racks/trailer, and finally a bike may work for some people, but it didn't work for me. People are all different. There isn't one "right" way of doing something, like starting touring, that is going to work for everyone.