I understand your stance on Biden. I am not a Hillary fan and absolutely detested her during the primary, but after seeing her speech at the convention, I was having second thoughts about keeping her off the ticket.
I think Hillary was left off the ticket for a couple of reasons. One, I think there are some issues out there will Bill Clinton and his Clinton Foundation that the Obama campaign was concerned about. Two, in light of the Edwards' story, I think the possibility that Bill had continued his philandering was an issue.
Finally, I think Hillary mishandled her exit from the primaries. After Obama won Wisconsin, Hillary literally had no chance of winning the primary. Yet, not only did she continue her campaign, she started making comments that McCain was more qualified than Obama. This was AFTER it was apparent that Obama was going to be the nominee. It was a hail mary on her part and it didn't work out.