The following is an excerpt from Wikipedia about Sarah Palin, the presumptive front runner for McCain's ticket.
"Palin holds a bachelor's degree in journalism from the University of Idaho where she also minored in politics. She briefly worked as a sports reporter for local Anchorage television stations while also working as a commercial fisherman with her husband, Todd, her high school sweetheart.[3] One summer when she was working on Todd's fishing boat, the boat collided with a tender while she was holding onto the railing; Palin broke several fingers.[3] Outside the fishing season, Todd works for BP at an oil field on the North Slope[9]"
Evidently, she is linked to big oil through her husband.
Now, she is not her husband. However, she has taken one of the tried and true paths to female Republican stardom - she was a news anchor just like Kay Bailey Hutchison before her.
Her beauty queen status (though McCain doesn't like celebrities!), her creds as a news anchor, and her attachments to oil more than make up, in Republican eyes, for her lack of testicles.
I think this choice is a desperate and transparent effort to make up for so much that is unglamorous about McCain.