I'm hoping for an iOS update tomorrow and new apps to follow. If Apple is indeed releasing a new update, it's very likely that devs are waiting for the new update before they release anything. If an update comes out and no apps immediately follow, I'm going to start doing some research and start emailing some devs to find out what the issue is. I don't see any reason why a simple game like Doodle Jump hasn't been updated for the display.
No, that has absolutely nothing to do with updates or any of that sort. The developers aren't waiting for any new updates, the SDK has only been out for a week (months for those devs using the sdk betas). They need time to actually code their application to support the higher resolution and some developers won't do this until they get their iPhone 4 in hand.
A simple game like Doodle Jump? Are you joking? If any of the graphics were drawn for the specific resolution of iPhone, it has to be redrawn again for the new higher resolution and it has to be fully tested to make sure it works. It's not simple at all.