The Ten Basic Rules to Improve Your Writing

[Omega22]

Of course if story is just one of thousand clones nobody will even look into one with bad grammar( probably almost nobody will read it in any case)
But If that story has extremely rare content you just have no choice it it happens that it match your fetish perfectly.

As for the brainpower comment, I feel that it isn't always related to grammar. For instance, a story could have perfect grammar and yet it could be overly complex to read. I think that has a bit to do with the talent and/or experience of the story teller in question.

I agree with that
if story is hard to understand and imagine then it will be real pain to read.
I think there is no way for native English speaker to mess grammar that much to make story unreadable, but for non English speakers this sometimes happens.

[Venom]

I agree with that
if story is hard to understand and imagine then it will be real pain to read.
I think there is no way for native English speaker to mess grammar that much to make story unreadable, but for non English speakers this sometimes happens.

Yes, sometimes punctuation, articles and all the other fancy stuff are quite useful.