Buying the game during beta will include all updates up until release, of course, and bug patches will be free.(emphasis mine)
The exact wording in question strongly suggests that, until Minecraft is considered "out of beta," we really don't have anything to worry about.
I'm not sure that's what it said before, though, so he may've edited that bit in. But it still sounds like expansions to me.
There will be a bigger focus on testing and stability as well, with more time between updates.
I think this may be the wrong way to handle it; I don't really see their small team catching bugs quite as well as the vast playerbase at large can, and the impression I've gotten is that a lot of people really liked the regular update schedule. It seems like it was always one of the first things people would mention about the game, and a lot of people were pretty upset when he was busy working on the halloween update and setting up the company.
Some players feel entitled to a fairly bug-free experience, while others are eager enough to see new features and updates that they don't mind things being a little rough around the edges.
So once voluntary updating is in, how about having two "feeds" of updates to choose from? One with stable yet (relatively) infrequent major releases, and one "use at your own risk" feed with whatever's on the cutting edge at the time.
Letting them choose which mentality they want to play by seems like the only way to please both, and as long the updates are incremental towards the next "major release" and don't get too far ahead of it, I don't think it'd be too much trouble to maintain.(based largely off the idea of Puzzle Pirates' test ocean, Ice.)