Why do Americans spell so many words differently from everybody else?

I don't understand why Americans changed the spelling of so many words. Eg. colour/color, centre/center, manoeuvre/maneuver. It's like trying to make words more simple. I think this is one of the reasons why everyone here in Australia sees Americans as being lazy. (I have nothing against Americans, it's just a mive stereotype here in Australia.) Also why do Americans invent words that don't exist anywhere else? Eg. 'dove' instead of 'dived' and 'snuck' instead of 'sneaked'. To many and I'm sure many people when I hear these words it makes me think of un-educated. I know it sounds like I'm hating on Americans but I actually really like America, it's very beautiful. I'm just curious as to these change spellings and words.