Why Not Winner Take All in the Democratic Primaries?

If the Democrats ran their nominating process the way we run our general elections, Sen. Hillary Clinton would have a commanding lead in the delegate count, one that will only grow more commanding after the next round of primaries, and all questions about which of the two Democratic contenders is more electable would be moot.
--Sean Wilentz

I've often wondered who would be ahead in the Democratic delegate count and by how much if Democratic delegates were awarded on a winner-take-all basis in the primaries. Wilentz poses an answer that I suspect is true, and if I weren't too busy (or lazy) to do it, I could confirm or refute my suspicion for myself. If Wilentz is right, I wouldn't expect Barack Obama's supporters to admit it, but I would expect Hillary Clinton and her supporters to shout it from the figurative rooftops and for the media to make a issue of it themselves. I wonder why they don't.

But even more importantly, why do the Democrats award delegate votes the way they do instead of doing it the way the Republicans do? It seems to me that the Democratic party should award delegates to its candidates the same way that electoral votes are awarded to the candidates in the general election. The winner should take all. To do it any other way seems like a recipe for failure, especially if the following assertion by Wilentz is correct:

The latest state-by-state figures (as of late March) updated from SurveyUSA, indicate that if the election were held today, Clinton would defeat McCain in the Electoral College because of her lead in big, electoral-vote-rich states such as Florida, Ohio and Pennsylvania -- and McCain would beat Obama.