Looking at the list of people at creator camp it's pretty clear they were invited for their specialties, mainly.  What are there -- three object makers?  And the rest are mostly people who do lots and machinima.

I don't say machinima isn't content: it's an art, too.  But it's one that can be done without having a way to edit game files in any way.

It's been pretty clear from the beginning of the hype for Sims 3 that they're really trying to get people focused on a certain range of activities and to talk them out of wanting to do other ones.  So I think they've brought in a bunch of people who they think might be convinceable that the range of activities they're making available are sufficiently awesome that they won't miss the others.

Though it's hard for me to believe that the best machinima makers are going to be satisfied with getting all their clips by following their Sims around the sidewalks of the town and hoping for the best.  Especially as it has been revealed that you won't be able to follow your sims into community buildings.  Just puzzling.