WoW and MMO's in general are a completely different category though. The whole game revolves around grinding... the actual gameplay is a pile of shit most the time.
I wouldn't necessarily state the game revolves around grinding, rather that grinding was added due to poor gameplay. Imagine if something like Devil May Cry, Ninja Gaiden, or God of War was multiplayer. I mean, the game could not be beaten without help. A major portion of the game should be community interaction, and not pointless grinding. I don't mind a little, but the question is, what defines tolerable? Similar to what you've already stated, some people can play for hundreds of hours before they get bored, others get bored after a few minutes.
Different strokes for different folks. I totally understand the people who just want to get in there and have everything available from the beginning and hopefully we get enough games that cater to everyone's tastes. The bit I don't understand is when people get in to the "get off my lawn" syndrome and refuse to accept not all people think the way they do.
That also is human nature. Not really sure if it's jealousy, ego, or spite, probably a mix of those and much more. My issue is with the developers here. Once a game becomes popular, everyone tries to emulate it. This in turn brings a downfall of other games. And I don't think it's necessarily because a new game is better, rather, that it's new. I'll admit, when the Playstation came out, I was getting sick of 2D platformers. They were everywhere. But new genres came out, and they almost went into extinction. The 2D platformers now though are kind of fun again. And it's not because they're better, but because I haven't played them in awhile. For about a decade, all we had were Quake style FPSs. Then Halo and CoD came out and took over.