[jimbob]

I'd think that the americanisms such as color and lite are introduced for two reasons. With the dropping of the "u" in many words (including but not limited to honour, colour, neighbour...) the americans were distinguishing/distancing themselves from their british "overlords" who spoke the same language. I'd imagine that had the lower colonies not had the rebellion/revolution, they'd be using the "u" just as much as their less independent neighbours to their north.

As to lite, defense (instead of defence) etc. I'd imagine that these are more the result of simplification for the sake of commercialism. The brits, having a major economic downturn combined with a weakened but significant aristocracy (which favours the status quo) have not embraced this whole-sale linguistic simplification scheme. We canadians have likely (through osmosis) taken the british lead without even realizing it!