[+/-] The 'Bush Rule of Journalism'

Check out what veteran reporter Robert Parry calls The Bush Rule of Journalism:

“Don’t take on the Bushes” is becoming an unwritten rule in American journalism. Reporters can make mistakes in covering other politicians and suffer little or no consequence, but a false step when doing a critical piece on the Bushes is a career killer.

So my question is why isn't failure within his own administration considered a fireable offense?