Why do polls show that the political race between McCain and Obama are that close?

I’m really confused by all of this…from what I hear is, McCain supports majority of what Bush does and what his plans are. With that said, Bush has a very low approval rating. How can someone support one person, but in turn give the person who he agrees with a bad approval rating?

What is going on with all of this? It seems to make no sense as to why it would appear this close. Also, I’m confused on the matter of how I’m hearing about 27% of Clinton’s supporters are now supporting McCain, which also doesn’t make much sense to me either. I know that Clinton and Obama didn’t see eye to eye on every matter at hand, but I’m sure Obama is much closer to her overall plan than McCain’s.

Can anyone help shed some light on these matters? I’ve really been a bit confused and bewildered as of lately about it all. It seems that the media may have twists on how they present all of this, and they aren’t letting in all the details on how they’re getting these numbers, I don’t know.