Why do people find it so hard to differentiate between "you're" and "your"?

I understand that there are frustrations about the correct use of the English language, but don't forget lots of people speak of type English as a second or third language. They make some mistakes, but are still miles ahead of who only speak English. I remember a conversation on EP, where a German guy and I where responding in a thread. There was one American who felt the need of correcting the German about a little mistake in his English. Another American jumped in for us, that our English was better then the average highschool student. I even see this in my job, our European HQ is in Scotland but every Dutch employee in our Dutch office uses better English than the Scots. Bottomline, do not be too hard at the rest of the world, when they do their best to keep up with you.