Ahh, yes, the HMS Rururu set alight in Boston harbor while unloading a bunch of printed Us and loading up a cargo of spoken Rs. To this day, Americans are almost as stingy with their written Us as the Brits are with their spoken Rs.

"British spellings" are an affectation Brits developed to make their language look more French and therefore more prestigious; Americans, who know we're the equals of France, kept the older spellings as recorded by Webster.

The "just so" story that I've heard is that post-colonial Americans have dropped the "u" from "-our" words for two reasons: efficiency, and to set them apart from the English.

I was also under the impression that the "efficiency" argument was at least partially influenced by Thomas Jefferson. I just did a brief search and I wasn't able to find reference to this online, but from my visits to his home at Monticello I recall that he had a unique style of writing - for instance, he tended not to use capital letters in his personal notes. He seems like exactly the kind of person who would have been vocally in favor of dropping unvocalized letters from words.

The 'u's are attributable to Dr. Johnson (and his desire to make English seem more French and therefore prestigious), but by the 18th century the cultures of Britain and America had diverged quite a bit. No 'u's were ever dropped - they were added - so I doubt this story. (Americans definitely liked setting ourselves apart, though.)