Quote: "unnecessaurily."
Hahahaha
To be fair it's not necessarily the British adding letters unneccesarily, it could quite feasibly be Americans dropping them out in a lot of the cases. Obviously for some of the more recent words, differences in spelling can come from anywhere, but we've actually had colours for example for a lot longer than America as we know it today.
I do quite like the thought of someone in the colonies sitting there looking at a letter and thinking "My, these sentences have far too many letters in. Makes it so tiresome to read. Right let's get rid of that one, and that one, maybe that one too..."
{note - some portions of post may not be entirely historically accurate}
"A West Texas girl, just like me"
-Bush