I would venture a guess that this is to make more accessible the Android platform to existing ActionScript developers. I can't imagine many Android devs would pay thousands to buy and learn Adobe tools when they can build the same software with the tools they know.
While I have no doubt it sneaked its way in though some means you weren't expecting, I've never seen air install automatically. It often is shoehorned in though flash, but there are numerous prompts about what it's about to do.
I got a mail from Adobe today as a part of the prerelease program. They'll soon have a private beta of Adobe air for iPhone and qnx for select developers (those who impress them with good apps for air for android, which will be shown at MAX 2010).