We can debate what obligations journalists should have, but they themselves spend lots of time meditating on the practices and obligations of their profession. Much of their own discussions about, say, whether it's appropriate for MSNBC to have liberals on or whether some particular story was "fair" or not is framed within this narrative of standards and obligations. That much of this discussion is often based on false assumptions or excludes important facts generally leads me to conclude that for all their talk of being dedicated to the truth, or whatever, when it comes to their own profession they're often quite full of shit.
And aside from whatever motivates journalists personally, there's also the issue of what motivates their editors, their publishes, and their parent companies. I know we all are supposed to maintain the polite fantasy that news divisions are somehow isolated from the business side - again, those professional obligations and standards! - but that, too, of course is bullshit. I don't know if what goes on at NBC is influenced more by Tom Brokaw's golfing buddies or GE's desire for government contracts, but it's long been obvious that there's more going on than a simple quest for ratings and advertising dollars at MSNBC.
