I mean really, what exactly is the advantage to having everything half the size?
Maybe this will help you understand.
Here's a full sized screenshot from Retina MBP at default resolution:

As you can see, everything is proportionally the same size as on a standard 1440x900 Macbook pro, but with more detail.
Everything that comes with the OS, pretty much all of Apple's apps, apps that use the standard Cocoa components for their UI, and all of the other apps that have been updated to support it in the last four months all draw with this higher detail.
Apps that haven't been updated yet (like Photoshop, which is supposed to be updated in the near future) display at the same size, just with less detail.