http://www.amazon.com/Press-edition-...sin=0262011530
As I tell my students, the MIT press version uses dark blue ink (really violet) on the cover, whereas the McGraw-Hill book uses light blue ink. Obviously, light blue ink is so much more expensive than dark blue ink as to more than double the price of the entire book.
Snark aside, the real reason is that textbook publishers gouge the textbook-buying public, and specifically the bulk-buyers. I tried to bulk-buy the MIT Press version, hoping to save money for my students, but I was told that only the McGraw-Hill version could be purchased in bulk (e.g. 100 copies at a time, for a course). I find this system reprehensible, but don't blame the authors; they've put the entire contents of the book on the MIT Press website where it can be read for free. I've met two of the authors and they are wonderful people.
Note that there is exactly zero, zip, nada difference between the two editions. They are identical except for the cover.