You are so wrong on this, it's hard to know where to begin.
You quoted Elton John as saying Hillary Clinton is trailing Barack Obama "in part at least, because of prejudice against women. I never cease to be amazed at the misogynistic attitudes of some people in this country."
You then took him to task by saying "if you believe that even a sizable number of the more than 13 million Americans who have voted for Senator Obama did so only because Senator Clinton is a woman, do you not also have to believe that a sizable number of the more than 13 million people who have voted for Senator Clinton did so only because Senator Obama is black? Is Sir Elton suggesting people cannot or do not support Clinton or support Obama based on their identities and policies and just on their demographics?"
Well, Keith, first of all, you don't have to believe that to acknowledge that misogyny and sexism has played a significant role in this primary season, and that the media has done quite a number of Clinton in the process. The so-called crying she didn't do in New Hampshire; the repeated references to whether she's likable enough, or whether her voice reminds men of their nagging wives; the she-devil horns Chris Matthews put on her head on his show; the "fucking whore" comment that cost Randi Rhodes her show; the finger-wagging episode you did when Clinton didn't get rid of Geraldine Ferraro quick enough to suit you; these things did not happen in a vacuum, and if you think that a voting populace that still gets its news mostly from television wasn't affected by its talking heads into believing that racist comments are bad, but sexist ones are all in good fun, then you're delusional, and you're smarter than that, Keith.
I don't believe that the majority of Obama's support comes from people who think Clinton isn't qualified to be president because of her gender. If that were the case, then the vast majority of his supporters wouldn't be willing to vote for her in November if she is the nominee--but they are. And the same is true in reverse.
I like you, Keith. You were a voice for the left when there was no voice, but you seriously need to look at your own sexism, because as one very prominent feminist has recently noted, you can't be progressive without being a feminist. The two go hand in hand.