True. But it's a bit thornier when it comes to a protected class like race, gender, age, etc. If you can show that the firings were racially motivated then 'at-will' doesn't matter.
And ordinarily I would agree with the posts about disgruntled employees 'playing the race card,' but if I had to suspect an athletic department of being racist it would be AU. The whole Eric Ramsey case started out because of Ramsey's exposure of a policy the AD had against black players dating white students...and that was the 1990's.