I know we all keep hearing about how Apple doesn't third party apps causing the iPhone to crash or whatever, but that is just lame and obviously far from honest. I think it is more likely that they have some technical limitations that are preventing them from supporting JavaME or some other standardized runtime, and they are not ready to roll out their own.
So I guess if I want to do map search on the iPhone, I better like using Google Maps. If I want push email to it, I better be using Yahoo Mail. I don't guess I'll be pulling down videos from YouTube or ESPN to watch on the phone.
Of course having a "full" browser on the phone is huge. Apple has to be totally committed to this at this point. Theoretically I can go to GMail directly on the iPhone and get the full AJAX interface we all know and love. Maybe there is some way to have it run in the background so I can get the email pushed to me. Of course I still can't go to Yahoo Maps, since it uses Flash ... Ditto with YouTube... Also, Outlook Web Access works ok on Safari, though it's not going to provide push email like the IE version would (or like you would get with a Blackberry.)
So does any of this matter? The most significant thing is that one can expect that support for Safari just became more important web developers everywhere. Not a lot more important, but at least a little. I don't think Microsoft or Mozilla have to worry too much about IE/Firefox users switching to Safari. It's big draw is speed, and Opera was already way faster than IE or Firefox. Plus it's got a lot of issues...