Your and you're / were, we're and where / there, their and they're?

I am a regular participant in an online discussion forum which links British and American Conservatives. I have noticed that many American people don't seem to know the difference between their and there, where and were, and especially your and you're. I would estimate that over 70% get it wrong every time. Is grammar, spelling and syntax now considered unimportant in modern teaching, or is this a sad reflection of how phonetic language is taking over our culture. The problem exists in the UK too, but not on the same scale. I notice that many US graduates make the same mistakes, even those from the best East Coast establishments with first cl degrees.