I have had similar problems too for stays in the UK, Euroland and Pakistan. Each time I have faxed/e-mailed and had my points adjusted.

For the UK stays it appears that they have simply taken the figure in sterling as dollars (ie exchange rate of unity).

I have asked Marriott to investigate why I have to apply for the remaining points. I received the following reply
"I have forwarded your account for review to see if there is a problem in the point posting process."