>>19
Abelson is less "pure." These days he talks about Python and consults for Google and in the OP's linked interview even claims that Javascript is the spiritual successor to Scheme. That worldliness isn't a bad thing per se and he still has a lot of interesting things to say, but there's something irresistible about those saintly types who stick to one incorruptible ideal which they doggedly pursue as far as they can go. One can easily imagine Sussman, ensconced in his office like a hermitage, happily hacking away at Scheme until the end of time; I don't think the same is true of Abelson, for all his merits. But all I know of them is through the internet, so it's possible that I've got the entirely wrong impression.
Incidentally, with Stallman's departure Sussman also seems to be the only founding member of the FSF still on the board.