Well, some people love to rate things a 1 just to be obnoxious..
It's a classic case of "relative scale," and one of the reasons that I shy away from public-rated things (public-rated game reviews, restaurant reviews, etc..). The 1-10 scale just doesn't mean the same thing to everybody. For some people, the 10 is almost unattainable, to be used only on the most godlike things (i.e. never). For some people the 10 just means "this is as good as could be expected." For still others, it means "relative to other offerings at the same level, this is one of the best." The same is true for the 1 on the scale; for some, it indicates something that is so completely and totally useless/horrible that you should run, screaming the other direction. For others, it means simply that whatever they're rating didn't meet their expectations -- not that it was horrible just disappointing.
People also approach the rating process with different philosophies. Some people tend to give every rating within the 5-10 range, where 5 really didn't meet their expectations. Still others think a 10 can never really be given, and tend to give on the 3-8 scale.
Finally, some people thing of the 1-10 scale as a method of protest/support voting. They give a 1 in protest of some minor thing, not really saying that the product is horrible, simply that they're irritated by something about it. They give a 10 if they support the product, even if they don't think it's perfect.
The sad thing is that most people don't realize how far even a single "1" vote takes down an average. Look at it this way: for every "1", you need 3 "10" votes to bring the average almost back up to 8...
It's also unfortunate that even though a lot of people are cavalier about voting on these ratings.. these same people will use the overall rating of a product to gauge whether they want to buy it..