Bootstrap is free. Designers are not. A custom design would be better (read: fancier) for my solo projects, but as it stands, my coding skills are sharper than my designing skills.
And what exactly is wrong with that? It's just a game of enticing.
Seems like different people will get a different read, for me it's a chance to participate on an exciting new product from well known developers and innovators. If I don't get in the first invites what's the problem?
It's 37signals. If you haven't heard of them before, you're incredibly lucky to be even allowed to view the webpage of the hipster gods. Let alone get a beta invite.