Quote Originally Posted by Papewaio
can any American tell me why your is not written yor by Americans?
Blame Samuel Johnson and Noah Webster. Here's a little more detail.

We Yanks merely continued a tradition the Brits started, sort of like the rest of our systems and values. For example, the British cherished liberty, so we fetishize it. The British marginalized monarchy, so we eliminated it. The British enjoyed bad food, and we perfected it. We just take everything a little further. It's part of our charm.