Too many competitors. You've got Silverlight. You've got Chrome. Both are trying to do the exact same thing. And AIR doesn't have much going for it beyond the fact that it got there first. Not many killer apps for it. Therefore, it doesn't get nearly as much attention as the much larger web sphere, which hasn't been relying on AIR for anything yet.
Silverlight is more of a Flash competitor than an AIR competitor. Chrome + Gears is kind of AIR-like, but it's a different approach to the same goal. More like Mozilla Prism.
I think offline/desktop access (whichever way you get it done) is an important step for the adoption of rich Internet apps.
I know it's bad to say this here, but I'm not really that eager to see rich Internet apps. It adds a layer of abstraction that doesn't need to be there, and I think development suffers when you're doing an Internet app rather than a desktop one.
I think the better solution is making desktop apps that emulate Internet apps. It's faster for the end user and it takes less effort for the developer. I think MobileMe is a perfect example of that. Make a powerful Internet app - but when you're not USING the Internet, just make sure it syncs with whatever app you're USING for your stuff.
