You don't have to worry about all the money spent on existing iPhone and iPod Touch games and applications, as Apple's confirmed they will all work on the company's new iPad device.
Apple has released an updated developer software suite for applications to better take advantage of the iPad screen. Out of the box, the iPad can automatically upscale the existing applications or run them at their existing resolution (which looks a bit silly, but it's an option).
According to reports from the event, some applications look better upscaled and others, but the consensus seems to be games look really spectacular on it.
(Please excuse all hilarious iPod/iPad spelling errors!)