^That's not really speaking anything about the system in that case, I think. In that case the factor that causes or removes the fun is the DM, not the system at all. I'm guessing that Josh is trying to put up cases where the SYSTEM is the cause of the lack of fun, and in your case it seems that the cause was the GM.
I DO see your point in fun not being I/O like that, though. That seems, again, to be a product of one person preferring a different GMing style. If the system is good, and it sounds like it is in your case, then that variable has been eliminated. The variable in your case is the GM, and if you don't have fun with one GM and do have fun with another, then the system is totally irrelevant in that case because you probably wouldn't have fun with the second GM regardless of system. Then again, if the GM ran a game in another system that you really enjoyed... maybe it is the system after all, that set up the possibility of a bad game.