I read several places that it is not unusual for a new administration to replace all US attorneys, like both Bush 1 and Clinton did. I have no idea how true that is.
What makes this case unusual and give the public something to sink their teeth into is that there was already a preliminary investigation, during which Gonzo swore blind they'd given the panel the whole story - and now it comes they were hiding several key facts. Not necessarily because it was not legal, more like they were kind of hoping no one would notice. Weird. It's like they assume everyone else is as incompetent as they are.