I actually wrote a blog post about this a while ago, called "imitation is the sincerest form of flattery" (http://goo.gl/K4RY) because I was hearing people complain that the site I was designing was too "similar" to other sites, specifically 37signals' product marketing sites. But who cares? They're good design patterns. You have to start somewhere.

And aside from that, building a promotional site is hard: http://goo.gl/8OlP. There's a lot of work there that's hard for a programmer to predict in advance, given that programmers generally haven't done things like think about how to market their product to an underserved niche. Tongue somewhat in cheek.