For BCS schools, the reason there is so much coaching turnover this year is due mostly to conference realignment. Pac-12 landing a whopping new TV contract helps lesser schools like Wazzu, Zona, ASU to afford going after big name coaches. That's why you see so many openings in the Pac-12 this year.
With A&M moving to the SEC, it's not surprising that they fired Sherman. Afterall he went 25-25 in 4 years. That's worse than Callahan who went 27-22. Not that A&M is hard up for cash, but the SEC pays more than Big 12, so it makes sense that they'll want to pay big $$ for a new coach to lead them into their new conference.