An excellently written argument. If we were going to develop a library of writing for people who aspire to turn RPG's into an art form to think about, this essay would have to not only be in there, but displayed promenently.
Mearls clearly explains something that I had noticed before, but wasn't able to elucidate - not every setting no matter how well crafted is gameable. I'd figured that out, probably alot of people had, but this is the first time I've seen someone been able to explain it by a general principal.