Prior to the Retina, they offered a 15" with 1680x1050; so that would be 1680x2x1050x2 (equivalent to 3360x2100). That's really what the MacBook Pro with Retina Display should be at by now, especially given the $2,399 price tag.
As for pixel doubling or HiDPI, that is still displaying pixels 1:1 on the Retina display, if you select 1440x2x900x2 (equivalent to 2800x1800). Using pixel doubling or HiDPI at a non-native resolution does make things look slightly fuzzy, as one Retina-size pixel must be split between two. I can notice it without a magnifying glass.