It has a "UI resolution" of 1440x900, yes. But the way the chrome in OS X is designed, 1440x900 is suitable for a 13" screen, not a 15" screen.
The previous high res option of MBP 15" had a resolution of 1680x1050. This (doubled) would have been a good resolution for the new 15" MBP retina display.
I have been using 1440 by 900 for years on my 2007 MacBook Pro, and I have no complaints regarding it. I have seen the high res version of the 15" and it felt too small to be comfortable to read.