Is it hard to make apps look nice with the iPhone 4's Retina Display?

[iLoveMyApple]

Like what does an app developer have to do to make the app look nice on the iPhone 4? The only apps I have that look good on my iPhone 4 are all the default ones, iMovie, Yelp, and Cro-Mag rally.
The great thing about the iPhone 4 is its amazing screen, but half my apps look fuzzy and crappy.

 

[CJayC]

They just have to replace their existing artwork with artwork that's optimized for the 960x640 resolution screen. Sounds easy enough but this requires a lot of developers to completely recreate their artwork because most only created their artwork to be optimized for the 480x320 screen.