THe crew may have been required to swap out because of the length of the delay, which may have pushed them past their maximum hours for the day.
But that's not what AirTran says in their detailed point-by-point response. They say that it is "not uncommon" to swap out a crew "for any number of reasons." They don't say which of those many reasons apply to THIS event. In a document whose stated purpose is to lay aside rumors and set out all the facts to dispel this "urban legend", they play coy with this very critical point.
Airtran mouths vague policy platitudes when they could have more easily stated the actual reason this crew swapped. They certainly chose not to waffle on other, far less significant points, clearly and emphatically denying them.
AirTran decries all the speculation, then makes a statement about the crew that actually requires speculation to parse. Does not compute.