In general job X, that may be true. But when you're being hired at a company where your job is going to explicitly be writing clear technical prose, I don't think it's unimportant at all.
Grammar is probably more important for sales than it is for developers. I get a few sales pitches and tend to dump the ones with poor grammar. I feel like: if they can't bother to send a clean pitch, how well are they going to manage my account?
