I wouldn't say that FOBOS and DA are very different. One is a carbon copy of the other and is an obvious attempt to cash in on the other one's success. Is it working? FOBOS doesn't seem to be selling too well.
DAC is dead now. The site closed down last night and all assets would be handled by NMA now instead. Was that comment in the credits of FOBOS intended as nothing more than just a jab at them or even a jab at the Fallout fan base as the creators of FOBOS pretty much just disregarded anything that could have been suggested to make the game better? Yes, they closed down the FOBOS forums rather than try to moderate it and try to obtain some feedback to improve the game (like removing thong lady or lowering the amount of excessive profanity). Technically, what Sammael said is probably right. Interplay was given no permission to use DAC or NMA's links in the game (and especially not when the links are intended as a joke or defamation) so they probably could be sued. Will they be sued? I highly doubt it.