That's interesting... I didn't realize this until you said it. I currently have the 15" MBP at 1680x1050. Buying the new retina display would be a downgrade in screen real estate, since it would show an equivalent 1440x900. Sure it would be crisper, but when I'm developing on my laptop, it's all about screen real estate.
In the worst case, the OS widgets will take up more space than you'd like. But for development most of your display is text, and you'll be able to significantly reduce the font size and maintain readability.
How so? The new one has a physical resolution of 2,880 × 1800 pixels. The density is higher, so text can be scaled smaller and still be legible. Are you questioning how large UI widgets will appear?
This is odd.