Marc Ambinder's scoop is that Jim Webb withdrew his name from contention from the VP job once the Obama campaign let him know about the specifics of their apparently fairly rigorous vetting process. This is interesting in light of some of the earlier rumors that one reason Hillary Clinton is unlikely to be the choice is that Bill Clinton doesn't want to fully open his kimono on aspects like Clinton Library donations.
I recently had a friend who applied for a job -- unlike many jobs these days, the materials had to be submitted by snail mail. This was a job in the design industry meaning that a portfolio is required, making the process relatively cumbersome.
To set up a hurdle where you require some minimum level of seriousness such that people need to get up off their lazy asses and go to Kinko's ... you'd think this would not be too much to ask of someone applying for a very good job in a down economy. But a few days later, the company mentioned that the application deadline had been extended by two weeks.
I'll bet that they get a better hire as a result, though. If you skip directly to the interview process after some loose scan of resumes, the excitement of the moment can take over, and it almost becomes a matter of luck as to who catches you in the right mood on the right day.
Where I'm going with this is that the purpose of making it be known that you'll have an onerous vetting process is not necessarily to prevent another Thomas Eagleton; many of these candidates have been exceptionally well vetted, including Webb, who survived one of the nastiest and most expensive Senate campaigns of the last cycle. Rather, it's to prevent another John Edwards, whose lukewarmness toward the ticket was unhelpful to John Kerry's chances. You want to make a candidate jump through hoops for you now, because that's what they're going to need to do for you for four months on the campaign trail and then four years in the White House. Jim Webb ain't that kind of guy, apparently, which should surprise absolutely nobody who knows anything about him -- but better to discover that a moment too soon than a moment too late.