I've read the news that the 2.0.x series will be maintained for a year (or a few years, I forget exactly), because of the need to provide a "stable" version for inclusion in some other packages.
I therefore conclude that I could continue to use 2.0.x and expect security upgrades for quite a while if I didn't need to keep up with 2.1, 2.2, 2.3, etc.
But what about 2.1.x?
Will Automattic support the 2.1 branch after 2.2 is released? (Scheduled about a month from now!) What about when 2.3 is released, etc.?
I understand that the current release schedule is going to be three or four 2.x+1 type releases per year, and in a couple years that could be 8 branches to maintain!