Michael Hastings tried that. His car crashed then exploded - possibly in that order depending on who you ask, or what theory you believe.
That said, it looks like the Sacramento coroner does in fact employ at least one forensic pathologist, so that lends a little more credence to the finding. Also, in these high profile cases there are often quite a few witnesses to the autopsy, which makes it more difficult to squash evidence.
And, yes, there are plenty of stories of people surviving a gunshot wound to the head, even remaining conscious.