Trek (and Ridgeback) support their dealers. You get a bike that has been put together by somebody who knows what's what, and, if there's a problem, you can take it back.
Consider the alternative. Dahon (distributed by Fischer) have fessed up to a problem with some of their 2008 bikes that is potentially dangerous. Now are the mail order companies going to get in touch with their customers, and arrange for the bikes to be picked up, fixed, and sent out again?