Mystic-Scholar:
"Basic spelling and grammar?" As in . . . what, exactly?
Well...having been in a couple of games where I have to regularly re-read sections of their posts in order to have ANY idea what they're actually saying...
I'd say it's a case of figuring out if someone's writing style is so far 'out there' that the amount of effort required to decipher their posts will never be outweighed by the fun of them being in the game. And that bar floats to different heights for different people.
I mean, I have a GM who routinely misspells words. His punctuation is terrible. His grammar is marginal, on a good day. But he tells a very enjoyable story, so I generally don't have to try real hard to summon up the enthusiasm necessary to figure out what he actually means when he puts the wrong word in a sentence or spells an NPCs name seven different ways in three consecutive posts.
There's a player in that same game whose spelling is pretty good...his punctuation is as bad or worse than the GMs, when he bothers to punctuate. And he apparently doesn't read anything past the first three lines of any post, even when it's your character directly addressing his character (in all fairness, he's getting better at that). But he does NOT tell an enjoyable story, and trying to follow his line of thought through a series of posts is almost migraine-inducing. If it was my game, he probably wouldn't be playing in it. As it is, I try to avoid one-on-one situations between our characters because it's kinda like listening to someone scratch on a chalkboard for an extended period when it happens.
So, yeah, I can see why a GM, who has to pay attention to EVERYONE'S posts, would potentially have some interest in making sure that their players had a writing style that was at least remotely enjoyable...or, at the very least, not painful to deal with.