A bike purchase is so personal, and potentially long-term, that you should always get the bike that fits best. It's crazy not to - you might move in a month, the shop closes or whatever, and you're stuck with a bike that doesn't fit!

That being said, you might ask your favorite store if they can order a Trek - they might not be an official dealer, but might be able to get it for you as a special order.

And, like others have said, they'll still get your loyalty with maintenance and accessories (although the store that you buy the bike might offer a year or two of tuneups on the new purchase.)