The iPhone 4 has a very high-resolution screen (for a smartphone) packed into a small space. The intense pixel density of 326 ppi means that the dots are so small that they're almost imperceptible. Apple markets this as Retina Display, and it's a key differentiation point when comparing iPhone hardware against other handsets.
Some figured that Apple would be bringing a Retina Display to the iPad 2, but that didn't happen and the current iPad still has the same 1024x768 resolution as the original model.
New hints have been discovered in the iOS 5 developer beta software that strongly suggests that Apple is prepping for something that has four times the resolution of the current iPad.
Graphics for the Apple's Newstand application on the iPad come in both the current 1024x768 resolution as well as 1536x2048. Artwork for the new Twitter framework also reference the new resolution. See screenshots of it at Techunwrapped.
Reuters this week also cited sources saying that the next iPad will have a new screen with five to six times the resolution.
These graphics could be just a test for Apple, but it wouldn't be a far leap to assume that iPad 3 will be launched with a high-resolution screen sometime during iOS 5's shelf life.
As far as people complaining about GPU performance in games, that assumes you're running at native resolution. And while that's optimal, it's not strictly required. People do more than game on their tablets, after all, and you shouldn't hold back on supporting a higher resolution for some things just because game playback can't run at those resolutions (look at the Xbox 360 and PS3!).
Some people don't see the value in a higher DPI, and that's fair enough. If you're content with the pixel density, then consider yourselves lucky--you have lots of great options on the market. For people who can tell the difference (and statistically speaking, that's most people), it's a compelling advantage.
Honestly people, try to be smart and objective about this stuff. I hate Apple but seriously, these arguments are just not thought through at all.