You are absolutely right in pointing out the lack of uniform probability distribution across the different pieces in McDonald's Monopoly game.

My goal in sharing the link above was to show that McDonald's Monopoly game is significantly more costly to win when compared to the Coupon Collector's Problem, which has an expected cost of O(n log n).

Still though, I think its pretty interesting that the folks who run the McDonald's Monopoly game have to factor in economics when setting up all of the probabilities as pieces get traded over the Internet (which is against the rules, but still happens as in http://cgi.ebay.com/2009-McDonalds-Monopoly-NORTH-CAROLINA-A...)