Those are outliers. For every assistant that makes that has sucess as a first time HC at an elite program, there are 10 that flamed out.
Also, several of the programs you mentioned aren't top-tier jobs. TCU and Louisville certainly aren't - they're exactly the HC training grounds that everyone is referring to. The jury is certainly still out on Muschamp as well.
There is plenty of evidence to back up the assertion that hiring a first time head coach at an elite program is a huge risk.
Don't know how many you have to have before they stop being outliers. Right now, in the BCS Top 20, at least nine of the top 14 (nearly two-thirds) are at their first HC job, including those ranked 3,4,5,6, and 8:
#3 Georgia with Mark Richt
#4 Florida with Will Muschamp
#5 Orebon with Chip Kelly
#6 K-State with Bill Snyder (of course, he's been there since 1089, with a hiatus of a few years somewhere in there)
#8 Stanford with David Shaw
#11 Oklahoma with Bob Stoops
#12 Nebraska with Bo Pellini
#13 Florida State with Jimbo Fisher
#14 Clemson with Dabo Swinney
Plus, Mike Gundy at Oklahoma State is at #23, and was a whisker from the BCSNCG last year.
And that doesn't count Gary Patterson at TCU, who's having an off year after a lot of success in 2011 and earlier.
Mike Price and Dennis Franchione had successful HC tenures elsewhere and ended badly due to personality issues.
Howard Schnellenberger drank himself out of the Oklahoma job after turning Louisville around and winning an NC at Miami when they were about to shut the program down for lack of success on the field.
The hugely successful Marshall coach (name escapes me at the moment) flamed out at Georgia, and is now facing prison time for fraud.
Bobby Petrino is a classic example of a hugely talented coach whose personal character issues make him a huge risk -- does a leopard ever really change his spots?
My whole point is that there's a lot of risk whenever you hiring a new coach, almost no matter his background. We got a HUGE break when the sun and moon and stars lined up just right and we had an essentially riskless home run hire with Saban.
You're absolutely correct when you say there are a lot of first-time HCs who have fallen on their faces (see Mike Dubose, Mike Shula, Ron Zook and Sylvester Croom). But there are also a lot of previously-successful HCs who failed at a new gig (Mike Price and Dennis Franchione, to name just two).
I don't really understand why, but it seems that in recent years there have been a lot of highly successful first time HCs. With that track record, I just no longer see previous HC experience as the absolute requirement I once did. Experience is good, but it's no guarantee of success. Lack of experience is something to overcome, but it doesn't guarantee failure.