The argument about RAM is just plain wrong. It only takes 12 megabytes
2048 * 1536 * (32 bits per pixel) = 12 megabytes
to store the display. 24 megabytes if it needs to double-buffer.
There's actually quite a bit of overhead at the CG* and Core Animation layers of the SDK that bump that up substantially. In the current iPad, it takes just a bit over 10 MB to store the image data for 1024x768 and have the necessary system stuff loaded into memory. I suspect that extra bit would not increase substantially on a 2x screen, but I'm sure it would some.
That's just for the framebuffer. All the intermediate textures flying around will need four times the memory too, and could easily eat up several hundred megabytes.