Their claim for any cut, much less a bigger one, seems questionable, given their argument that Zuckerberg stole their idea while he coded for their idea (actually a dating site rather than the social network that Facebook has become).
I wasn't aware that an idea was property, much less protected property, so I suppose that Zuckerberg capitulated rather than carry on fighting to avoid unnecessary unpleasantness. He must regret that decision now.
In any case, the real story with Facebook is how this kid created this major success story in websites. The idea for it is a tiny part of the total. The real genius was in creating the organization that has gone on to be so hugely popular -- finding the right people to staff it and the financing for a really expensive investment -- to become the major public spokesman for the company, to get the technology right, and to make most of the many difficult decisions along the way. Unless he had a guiding partner, he has to be considered brilliant.
This is a case in point, supporting the thesis of Techdirt's Mike Masnick that concept always plays second fiddle to execution. Someday, the story on how it was done will have to be written in a lot more detail than we have been given so far. It should be a great read.
It also seems to be a lesson in how intellectual property rights can get abused by the threat of legal proceedings that lead the party in the right giving up.