There's typing the wrong thing because your fingers are all over the place (last night as an example I think I typed: U ciykd yse a gaste L( - yes, my right hand missed the home key ... and there's typing the wrong thing because you don't know any better. In any case, if I know what they mean I'll not bother to risk upset by correcting them.
I think we all know there are many non-native english speakers out there... but what really scares me is that the majority of those mixing up there/they're/their ARE native english speakers. In fact, I'm pretty sure I see better word selection from the non-native speakers, presumably because they're actually taught english rather than picking a significant proportion up from peers, complete with bad habits.
Now, without further adieu, ect ect, I bid you ado. *twitch*