Aww... they did it for the kids! This quote is from January:

“We’d actually like to,” he said of making Jolie his wife, “and it seems to mean more and more to our kids. We made this declaration some time ago that we weren’t going to do it till everyone can. But I don’t think we’ll be able to hold out. It means so much to my kids, and they ask a lot. And it means something to me, too, to make that kind of commitment.”

A million confirmations here:

http://news.google.com/news/more?pz=1&cf=all&topic=e&ncl=dL5dXPM5Jj-g5iMs4kaA8GOTIokDM