I guess the bigger problem is the straining of the eyes to read things, and less so the cramped screen. I can deal with a lower screen real estate, but having a hard time focusing and reading is a problem.
I can't really tell if the fonts on the 13" are smaller, but the fonts on the 15" do seem to be a bit bolder.
That being said, it seems to be getting a bit better the more I use it.