It is difficult to conclude that there is something wrong with the current coaching model in the NFL.

For a start, here is the list of Superbowl-winning coaches who recently left teams and are currently sitting out:

Brian Billick
Bill Cowher
Tony Dungy
Jon Gruden
Mike Holmgren
Mike Martz
Mike Shanahan

The interesting thing to note here is that Dungy, Holmgren and Cowher all walked away from the game, they were not forced out or fired.

In the "unlikely to coach again but that is not certain until the coffin lid slams shut" category we have:

Mike Ditka
Jimmy Johnson
Dan Reeves
George Siefert
Marty Schottenheimer
Barry Switzer

Former Head Coaches on NFL staffs:

Cam Cameron
Dave Campo
Scott Linehan
Rod Marinelli
Mike Mularkey
Mike Nolan
Gregg Williams

Former head coaches currently sitting it out or employed elsewhere

Romeo Crennel
Herm Edwards
Dennis Erickson
Jim Fassel
Chan Gailey
Dennis Green
Jim Haslett
Lane Kiffin
Bobby Petrino

This is a pretty long list of top-flight coaches. This does not include other coaches who decided to pass up the opportunity of being an NFL head coach and instead moved to the college game (Charlie Weis, Dave Wannstedt). Add a couple of other coaches who tried out the NFL and decided that college was more fun (Steve Spurrier, Nick Saban).
Right now, because of the trend towards hiring younger coaches, we have a number of NFL head coaches in their early to mid 30's. This clearly can work (see Mike Tomlin in Pittsburgh) if there is continuity in the coaching staff.
In addition to the massive number of former head coaches either bouncing around other jobs or sitting on the sidelines, the firing of 3 offensive co-ordinators in one week in pre-season is unprecedented.
In the case of the Buffalo Bills, the firing of Turk Schonert is probably a result of results pressure on head coach Dick Jauron, who will almost certainly be fired if the Bills do not make it into the playoffs. The fact that Jauron and his assistants were summoned to meet with Bills owner Ralph Wilson suggests that they are collectively operating with a very short rope that could rapidly tighten to a noose. The poor performance of the Bills' new no-huddle offense in pre-season left the Bills looking for answers, and firing the OC is a pretty good answer, for now. Whether it will improve the operation of the offense, only time will tell. The remainder of the offensive staff is inexperienced, which does not inspire a lot of confidence. Even with Terrell Owens, the Bills offense is unlikely to strike terror into opposing teams. They may simply double-team him out of existence, and then rely on the overall mediocrity of the rest of the offense to throttle the Bills and win games.
In the case of the firing of Chan Gailey by new Chiefs coach Todd Haley, this can be explained in terms of Haley being a coach with an offensive background who wants to call the plays himself. This is not new in NFL head coaching circles. A lot of head coaches call or called the offensive plays themselves. Thinking of past coaches we have Bill Parcells, Mike Holmgren, Mike Martz to name but three. Gailey was a holdover from the Herm Edwards era, but sooner or later Haley and he would probably have clashed over offensive play-calling, especially since Gailey is more conservative than Haley.
The case of the firing of Jeff Jagodzinski in Tampa Bay is the most puzzling, but also in many ways the most revealing. Although Bucs coach Raheem Morris seemed determined to obfuscate over the real reasons for Jagodzinski's dismissal, there were plenty of leaks from with the Bucs organization attempting to explain the underlying reason for his firing.
Most of the reasons however, appear to me to be symptomatic of the fact that Jagodzinski, unlike many other NFL coaches, seems to think that a head coach is there to set direction, and then get out of the way and let his assistants coach. He deferred most of the play-calling and coaching details to his assistants, only providing directional input on plays. This apparently led to issues when the Bucs tried game simulations, and the multiple coaches involved in relaying plays to the quarterback led to delay of game penalties. However, by all accounts, the Bucs additionally wanted him to be wading into all of the little details of running an NFL offense, going beyond the zone-blocking scheme for which he had become known from his previous NFL time with the Atlanta Falcons. When he declined to do that, the conclusion that the Bucs seemed to reach was that he was in over his head.
While the firing of Jagodzinski sounds like a classic mismatch of expectations on both sides, it is also revealing. The NFL coaching model appears to place a high premium on head coaches and co-ordinators engaging in detail coaching activities. Jagodzinski, who came back into the NFL from Boston College, where he had been the head coach (but was fired after he interviewed for the vacant New York Jets head coaching position), seemed to have evolved a model where he delegated a lot of detail work to his co-ordinators and position coaches. This apparently did not sit at all well with Raheem Morris or the Bucs front office.
From observing recent events, it appears that offensive co-ordinators who try to delegate too much detail work being labelled as incompetent or out of their depth, while co-ordinators who are working for a head coach who was previously an offensive co-ordinator risk being emasculated, and ultimately rendered disposable. It is interesting that we do not see the same model of head coaches calling defensive strategy in games, even though a lot of head coaches have defensive backgrounds. Most head coaches are content to have the defensive co-ordinator run that side of the team.
All of which suggests to me that the overall coaching model, when compared to a conventional business, is decidedly dysfunctional. It also appears that the youth movement in coaching has taken over to a ludicrous extent, when coaches like Mike Shanahan, Jon Gruden, Tony Dungy and Bill Cowher are sitting on the sidelines collecting money from their previous franchises for doing nothing.