hi Sarah,
yes you're definitely right about all the differences you listed... but I was
actually referring to a period (after 1776) when the first only graphical
modifications were introduced for political reasons into the official language
of the newly born US. but obviously every immigrant spoke his English variety
according to the region of provenience (Wales, Yorkshire, Ireland, Scotland,
Cornwall...): this differences then contributed to the following evolution, also
in terms of vocabulary and structure, of American English.
I was certainly wrong about the spelling -ize (but I still believe it's more
used in US than in Europe, though it's not a rule), but, as someone who's
mother-tongue can confirm (since I'm Italian), I think the spelling -or instead
of -our (or also "theater" instead of "theatre") is actually a national
peculiarity.