I'm a little surprised at the disappointment throughout the blogosphere.  Here's my case for why Kubiak selected Bush without devoting much time to interviewing. 

Casserly et al. lasted a while, but no more than six years.  We're already entering year 4 of the Smithiak regime.  Kubiak needs results on defense NOW, not three years from now, and the only way to do that is by bringing in someone who is very familiar with the defense, knows exactly what the players can do, and more importantly, knows exactly what the players can't do. 

How else will the incoming DC understand precisely the holes that need filling in the off-season?  Does anyone else remember Kubiak's experience with David Carr?  He saw Carr tape and thought he could still turn him into a great QB.  It took Kubiak until the Oakland game in 2006 before he finally came to grips with the futility of making shell-shocked Carr into a top shelf starting NFL QB.  In other words, Kubiak has learned firsthand that merely watching tape doesn't give an incoming coach an accurate enough sense of the players' abilities and limitations. 

Plus, this coming season is critical for the franchise.  The following players have contracts expiring in 2009:

Chester Pitts,
Kevin Walter,
Will Demps (blech),
Kris Brown,
Demeco Ryans,
Matt Turk,
Ephraim Salaam (double blech),
Tim Bulman, and
Deljuan Robinson

The following players are free agents, restricted or otherwise:

Dunta Robinson,
David Anderson, and
Owen Daniels

I'd be happy to see some of these names go.  But most of them, like Chester Pitts, KEVIN WALTER, Kris Brown, DEMECO RYANS, Matt Turk, Tim Bulman, DUNTA ROBINSON, OWEN DANIELS, and David Anderson represent some of the few bright spots on the team.  Plus -- though no one much talks about it -- the team has to decide whether to exercise a pretty big option on Schaub.  It sure would be easier to decide whether to spend this money if we move beyond 8-8 mediocrity.  Otherwise, Kubiak will be hard-pressed to convince Smith or McNair that they need to open up the wallet for all of these players.

My point is strengthened still further because I believe that the team assumes it will franchise Dunta (though probably trying desperately to come up with some mutually beneficial arrangement) and rely on signing him to a contract in 2010.  And Steve Slaton will likely demand a new contract to match his incredible performance, if not for 2009, then for 2010.  Those are two upcoming major expenses that the regime will need to justify to McNair. 

Ultimately, I just don't think Kubiak could afford to wait another year before seeing results in his defense.  Heck, I think we're only two or three players on defense away from making a run through the playoffs.  Hasn't anyone else seen our offense?  Why aren't we crying out for a playoff team next year?

Yes, it's possible that some DC out there could have made an immediate impact during the season.  Some people will point to Gibbs' experience on offense.  True, by the end of the season, Gibbs had done a phenomenal job, but the running game didn't start to gell until a few weeks into the season... too late to salvage a winning season and too late to let us make a playoff run. 

In the end, who has the best chance of making an immediate impact on the defense?  The answer is plain and simple: Bush.