The deal the writers had to settle for was shit, the producers are already reneging on it, and they've refused to make even a single concession in four months of negotiations -- so I certainly don't blame SAG for wanting more.
At the same time: strategically speaking, I'm not sure this is a great idea. We saw how well big media got through the Writer's Strike (pretty decently) and now SAG is stuck with the lousy deal the DGA and WGA already signed off on as pressure. It seems to me like it'd be much better to sign on, ride low until the next contract period begins, and then enter negotiations to get all three guilds to strike at the same time -- hopefully after the recession has lightened.
BTW, this thread is a perfect illustration of why people get fucked over so hard by their employers in this country. All the big media bosses have to do is say "yeah, but we refuse to negotiate or budge on any of our conditions, even though they would make it impossible for your people to support themselves in the future" and everyone calls the union greedy and tells them they should settle for whatever scraps they've already got. :lol