I think there were several factors:

McCain couldn't run/manage his own campaign. Buchannan himself said it was a very poorly run campaign, especially in comparison to the efficiency of the Obama campaign
McCain couldn't get a message that appealed to both the fanatic base and the moderates
Palin is as swift as a brick. The fact that she could be a heart attack away from the presidency was terrifying to a large part of the population.
McCain's tax plan was pretty much panned by a majority of people with an economic education
McCain's rhetoric was not well suited for the current international climate
The list goes on...

While I'd have to agree at least McCain would be better than Bush (Palin would be a step in fufilling the Idiocracy prophecy though), Obama has had what the American electorate decided to be the far superior vision to run the country. And if how he ran his campaign is any indication of how he will manage the country, I feel rather confident in his abilities.