Interesting read from Quirks Mode, on how the iPad 3’s display will actually hurt the mobile web in particular, by creating a demand for larger downloads to accommodate for the hi-resolution screen.
In order to display properly on the iPad 3, all graphics of both web apps and native apps must be doubled in pixel density, which means their size roughly quadruples. Clever compression will solve part of that problem, but not nearly enough.
The problem is even worse with the mobile web. Jason Grigsby delved into the way Apple itself serves Retina-optimised images to its new iPad site. Essentially, they download the normal images first, and if a check for the iPad 3 is positive it then downloads the optimised images.