The article that Dr. Hadar notes on the main blog contains an interesting item that I have seen mentioned before, and I think it helps explain another reason why Palin prevailed over the others:

Others in the inner circle favored Mr. Pawlenty or Mr. Romney. Ms. Palin had no strong advocates in the group, an outside adviser said, but she had no detractors, either.

Something that longtime observers of McCain know is that he likes for his staff to be composed of people who are all deeply loyal to him and who vie with one another for his favor, which leaves McCain maintaining an uneasy balance among the rivals.  This is one reason why his campaign has been such a disorganized circus for so much of the last year and a half and why it has had such difficulty elaborating a consistent message.  The VP selection process seems to have been subject to the same problem of internal rivalries among advisors, but in this case the same dysfunctional squabbling that has weakened the campaign so far was greatly intensified.  This is not unique to McCain, but it does help to explain why Palin’s name rose to the top: there were no strong Palin supporters or opponents in the campaign, which meant that McCain would not be endorsing or snubbing any of his advisors by picking her.  She was the lack of consensus choice, and the one least likely to spark a civil war among his own top people.  His advisors may not be thrilled with Palin, but none of them is furiously hostile, and so McCain has managed to keep a modicum of order in his own camp. 

How close McCain really did come to picking Lieberman  is either the most hilarious or the most frightening thing about the article.  Had he chosen Lieberman, he would have lost in a rout after revealing a very Bush-like instinct to reward old friends and loyalists with key positions.  Given the likely alternative, Palin was the safe pick.