David Chaum is American, which wouldn't explain Satoshi's use of British spellings. For example, glancing over his last posts in the forums I've found one (
https://bitcointalk.org/index.php?topic=1790.msg28715#msg28715) where he writes "modernised" and another one (
https://bitcointalk.org/index.php?topic=1850.msg22952#msg22952) where he uses "formalised". It'd be very unusual for an American to use these "-ise" spellings that appear in Satoshi's writings. Add to that the fact that he inserted a quote about British bank bailouts from The Times in the genesis block, and it looks like Satoshi is probably British or must have had a closer connection with the UK than with America.
Well, The Times is possibly the most well known British newspaper outside of the UK, possibly because it's also one of the longest established titles globally. These things don't prove much, british spelling is not hard to enforce, just change the country setting in your OS. Even if he had exhibited some less superficial knowledge of Britain or use of British spellings or expressions, it's still not much to go on. It'd be fairly hard to guess someone's nationality purely on prose and content alone, try it with a someone else on the forum.