The physical resolution of the new MBP Retina is 2,880 by 1,800, but in fact at the highest resolution setting it actual uses a logical resolution of 1,920 by 1,200.

The mismatch is explained by this: For normal use, the screen uses more pixels to render text and graphics, keeping them at a readable size, but more sharp and crisp.

Games and other software can utilise the full resolution if needed. The article below explains more.

Forget Retina, look how much the new MacBook Pro displays! | Common Sense Tech – CNET News.

This isn’t quite what I was expecting, but then anyone who’s seen the difference between the new iPad 3 Retina screen and the old models will realise that Retina is the way to go.