Campfire, I think, is still a much better app than Google Talk, partly because it gives the chat so much space to breathe.
And I don't think all PROGRAMMERS care about that, but a significant number of DESIGNERS do.
Besides that, they already have products that implement large parts of 37Signals's applications' functionality. It is just a matter of them packaging it all up into something more usable and then marketing it. A large part of 37Signals's success is due to marketing; Without Signal vs. Noise nobody would know about them.
37signals IS successful because their stuff is minimal, which, again, is why Google would eat their lunch.
It sort of fills the minimum requirements for webchat.
I think if google decided to put some effort into chat they could create something pretty cool, hooked into all their other systems etc.
Huddlechat worked pretty well, and it was frankly amazing they took it down IMHO.
37signals should be (and apparently is) afraid of simple integration with the Gmail/Google apps suite by Google.
They would eat 37signals lunch.