"Another Edit: perhaps, when something like Google Gears is everywhere, it might change. But offline support - both for code and data - is kind of essential."
HTML 5 includes a storage API, including a SQL database. Apparently the iPhone already has it, and any browser based on WebKit (Nokia, Android?) will likely have it in the not too distant future.
Europe is way way ahead so perhaps that is where the difference lies.
I don't know about processor speed, I can see some intensive 3d special effect games needing native, but for puzzle games, or most 'apps' javascript in a browser is pretty much there.
The fact that internet connectivity on a desktop vs. on your mobile device is different by an order of magnitude. When you get ubiquitous and fast internet on the mobile device (not some bizarre spotty coverage), then things will change. Maybe Europe is ahead in regards to that, but in the US, I don't see that happening very soon.
Edit: oh, and also the processor speeds. So, basically I will bet on webapps for mobile after 3-4 years. Until then, at least, installable apps will work better.
Another Edit: perhaps, when something like Google Gears is everywhere, it might change. But offline support - both for code and data - is kind of essential.