sure the UI isn't as sharp..but its no worse than the old low res screens...you just notice it because it is butted up against perfectly clear UI.
Umm...it is worse in comparison to the perfectly clear UI and it is worse when compared to the same image on a non-retina display of the same size.
To understand this clearly, consider the following scenario:
Put a non-retina MBP and a retina MBP side-by-side.
The MBP is on the left, 15", 1440x900 (a.k.a., 1-to-1 pixel mapping).
The rMBP is on the right, 15", rendering in 1440x900 mode. (a.k.a, Best for Retina Display)
Now, you load a Web page that shows a 100x100 pixel image.
On both screens, that image occupies the same area.
However, on the MBP, that area is 100x100 pixels, while on the rMBP, that area is actually 200x200 pixels.
Now, the Web site didn't serve a 200x200 pixel image, so what did the rMBP do to turn a 100x100 pixel image into a 200x200 pixel image?
It used interpolation.
Images scaled up using interpolation do not look as good as their original.
I think that is as clear as I can explain it, alas.
So, updating the apps to suit the rMBP is comparatively easily, when considering that the entire Web needs to be updated for HiDPI displays.