Adobe's been opening the PDF for awhile. Basic specs have been free for all for awhile. Considering the fact that PDF printing is available as a "value-added" feature in both Office and OS X, this is pretty much the next big step for them.

If they don't open up, experience says a new open standard will eat their lunch. Might as well push ahead of the wave (or whatever the proper idiom is).

Or a pseudo-open one -- Microsoft's XPS format has had some push and was submitted to ECMA not too long ago.