I actually agree 100% - I wish that they had gone with discrete graphics on the 13". It is not enough, however to make me eliminate the rMBP from my list. It was hard not to go with the 15".
In my case I ordered the rMBP for a very specific reason. I want to move back to a 13" screen from the 11" MBA and I need the machine to be portable. I travel a ton and while the 15" is clearly a better choice with regards to "bang for the buck", I have owned a 15" in the past and traveling with it is a royal pain. I have no problem paying extra for the retina screen and more powerful CPU (comparing the 13" MBA vs rMBP 13") as the screen, in particular, will change my computing experience for the better. End of story.
All of the blanket comments around here regarding what a terrible ripoff this laptop is are hilarious.
I did agree first and ordered it.
Then I went to test it and even scrolling a simple 30Mo pdf file with pictures (such as technical review) is a pain... On my MBA11 it is completely fluid :-/