web2.0 apps is a funny name for dashboard widgets. they needn't be online as such, they just run 'within' a safari shell (remember, they needn't have the safari UI). they're just going to be widgets. you can make quite a lot with widgets.
i think this is going to be like voice recording and in-line mp3 encoding, other mp3 players have this ability, the iPod doesn't. the ipod has quite restrictive features compared to the competition, but they realised that feature creep doesn't make a good product. the iPod is spartan, simple, and clean. and has sold 100m units as a result. if you really want third party apps, get a treo.
i think the iPhone/Treo argument will resemble the iPod/iRiver debate quite similarly.