How can a movie with so many bad user ratings have such a high OVERALL rating?

Rating: 5/10 (2 May 2009)

My wife and I saw this movie after seeing IMDb's high (7.3) user rating. We were extremely disappointed and would rate it a 5.5 at the most. What's most distressing to me is that I am GENERALLY in COMPLETE agreement with the overall user ratings that IMDb users give to movies. I rely on these ratings to choose movies to watch. If a movie has an 8 or higher it's almost guaranteed to be a great movie that I will enjoy and remember for a long time (with the possible exception of older movies that are rated highly for historical significance). If the movie is between 7 and 8, I anticipate an excellent movie. Ratings between 6 and 7 are a little more circumspect. If the movie is about a particular topic or genre with a big following (e.g. a western, or a NASCAR race film, or a children's cartoon, or a science fiction film) then I'll adjust the overall rating by perhaps a point, depending on how much I like/dislike that genre of movie. Movies below 6 are almost always boring or painful to watch and are generally just a waste of my time. I felt "Burn After Reading" was very disappointing as a comedy and dreadful as a drama. The only somewhat amusing part was the last scene. In looking through a few hundred of the latest reviews, it appeared to me that most people thought it was a bad movie, with just a few users rating this movie a 9 or 10. Those glowing reviews look like they were written by the cast or production crew of the movie (or perhaps their family) with a financial or emotional stake in its success. While I expect the first 100 reviews of a movie to be highly positively biased, I generally trust the ratings of films with over a thousand reviews. So ... what happened here? "Burn After Reading" has over 64,000 votes and a rating of 7.3, but a large percentage of the latest reviews were (like mine) fairly negative. Has someone figured out how to scam the voting process? ... or ... Is this a movie that people either love or hate? I'm very concerned that someone has figured out how to scam the system so that movie producers or interested parties can buy a high rating.
If the voting is being done fairly, I can fully accept that I rate a movie differently than others. What I can't accept is a system that allows for buying or manipulating ratings.
I would like to see IMDb provide a feature where a user can see a histogram of the user ratings. Perhaps then we would see a bi-modal distribution for this movie, revealing that people either loved this movie (9s and 10s) or didn't care for it (4s, 5, and 6,). That might then explain the puzzling votes I've observed.
A further refinement would be to have statistics that show if all the great ratings came from users who enrolled at the same time or some other characteristic that points to a manipulated voting process. It would also be very helpful to be able to look at a random sample of reviews. With 64,000+ reviews, I can't accurately assess the quality of the rating or reviews by looking at only the latest entries. A random sample would be a great way to look for irregularities in the voting process. Finally, there should be a way for users to flag suspicious votes to IMDb for someone to review for irregularities.
What do you think?