I'll admit that I never heard any confirmation that they'd been signed, but I kind of forgot to keep an eye out for that. It seemed like a formality at that point. And then...
You may have heard that Samuel L. Jackson made an appearance on a late night talk show recently and said that he hadn't been contacted about appearing in the sequels...and that Mark Hamill hadn't either. And neither had Ewan McGregor.
Some of this makes sense. Rampant rumors notwithstanding, these actors appeared decades apart in the originals and prequels, and it would take some serious gymnastics to artfully work them all in.
But we all thought Hamill was a lock, didn't we?
Seems like maybe Abrams & Co. aren't as sure as the rest of us were (and "the rest of us" apparently includes George Lucas).
While we're on the subject of the Star Wars universe...have you seen this video plea to J.J.? Apparently, Abrams has, and says that he's largely on the same page with fans.