Yes, Language evolves and spellings with them naturally change over time. Many of the American English spellings were changed by design. There were several attempts to simplify and standardise English, some of which were more successful than others. Attempts were also made this side of the pond (the UK) but these were generally ignored. I guess the difference was because the USA had people from many nations so simplification of the spelling rules were more important.

A quick google took me to : http://www.bartleby.com/185/35.html