It's probably a lot of "coulda woulda shouldas" on the part of the voters. When a candidate endorses someone else, their voters don't necessarily go to that other candidate. They go to whomever they like the most. Remember, those are POLLING numbers, not numbers of actual VOTES. Thus, Dean may actually have gotten more votes than you, even though just about everyone who didn't vote for Dean prefers you over him. It's a flaw of the voting system. I've had it happen to me before and yeah, it sucks a lot.
Just a couple of (maybe simple?) similar things. A hands-off mode would be nice if it's possible, as well as the ability to convert to hands-off mode if you're eliminated during the primaries and don't become the running-mate. Giving a choice to endorse another candidate during the convention (if you've been eliminated) would be nice, and I'd also like to see the "everyone eliminated but the top two" system replaced with a "round" system -- eliminate the last-place candidate, then second-last, then third-last, etc. It would be more realistic and work really well, I think.