Dejan Kovacevic's piece this morning on the firings of Joe Kerrigan and Gary Varsho contains as much about these moves as we're likely to ever learn. It looks like what happened here was that Kerrigan and Varsho didn't respect John Russell's authority, and if Russell is going to be the manager, you can't have that. It also sounds as if the Pirates aren't too concerned about losing Kerrigan, in particular, on a baseball level. He came to the Pirates with a terrific reputation, and while Kovacevic's article suggests that Kerrigan's stat-centric approach might be better suited to a more veteran team rather than one that needs to develop its pitchers, it's worth pointing out that Kerrigan did preside over the development of Pedro Martinez, Derek Lowe and Kirk Rueter. And it's not as if Kerrigan's approach of fussing more over opposing hitters than on the pitchers themselves was a secret before he was hired. In any case, he does deserve to be fired if he was insubordinate towards Russell.
Ray Searage and Jeff Banister will replace Kerrigan and Varsho, respectively, on an interim basis. The Pirates all but anointed Searage as Kerrigan's eventual replacement in the offseason, so it's no surprise that they would pick him, and I imagine he'll probably stick in the job after this year as well.
These moves suggest that we can probably forget about the reports from a few weeks ago that Russell was on the hot seat. If the Pirates wanted to fire Russell, indications that he had lost his authority over his coaches would have provided the Bucs with a very convenient excuse to let him go. Instead, they're allowing him to take credit for firing two coaches. This suggests they still believe in him and that he'll be with the Pirates for a while.