You are right in that they have sustained HC tenure, which creates stability for the program and a continuity of philosophy for the kids. But staff under the HBC changes all the time, everywhere. Not just for salary reasons, more often there are performance vs expectation issues, or possibly just philophical issues, sometimes there is arrogant bastard (sorry, WM personality type) issues, and sometimes it's a chance to jump at a better option.
We've had 3 different HC's since 2007. Unarguable. LSU has discussed making the change, despite getting a NC. How many have TN gone thru in that time frame since they got rid of the fat pumpkin? It hasn't led to success, unless we're counting moral victories. How many schools have stuck with coaches but aren't bringing the team to the top level (excepting a few years given a star player like USCe with Clowney and aTm with Manziel)? It's a decision ADs have to make - do I stick with the guy and give him more time to work it out, or do we hit the reset and try again...and if we do that, what are our available options? Its a crapshoot.
The comparison is the HBC we had was sht at being a HBC and building a staff (and the fact that Foley gave him TOO many years to try it). THAT was a major reason for the turnover of staff in the past several years. The other SEC programs you mention, they have had turnover as well. AL has held Kirby for 8 yrs, but how many changes have they had on the offensive side? We've got two coaches that served as OC there under Saban. Richt was long standing, but he's been cycling thru OC's as well with Sablehouse, Bobo, and who knows what other circus animals. MSU is on their 3rd DC in 3 yrs, I believe, and perhaps their 6th in 8 yrs? Spurrier was swapping DCs trying to find something that worked beyond having Clowney on the field, and Miles lost his DC as well. Auburn? Plenty of turnover below the HBC, enough to drive them to hire Muschamp.
Again, how many 'brand name, proven coach(es)' have been out there that would come here? Yeah, we could have been gouged and overpaid for a name, and it might still not turn out (ie, Spurrier could have squeezed USCe to the breaking point based on his name and 'proven' record). Which is worse - paying what you have to in order to land someone you think is the next winner, or overpaying based on the name? For either, you still have the risk of it not working out.