Corn says a likely reason for Time's actions is that it would've cost them money. I did actually know that. What I really meant was that I didn't understand how this decision fits within the mythos of the "media protects their sources at all costs." Cooper was, presumably, willing to actually go to prison to protect his source. However, Time is likely not willing to sacrifice a bit of cash for the same reason.
The point is that it's a longstanding tradition that the ethics of journalism require that journalists protect their sources to protect their profession. In one act, Time has basically thrown this concept out the window. It no longer matters if journalists are willing to protect their sources. Those who pay their salaries (some of those, anyway) won't back them up, so the commitment of the individual journalist is largely irrelevant.
And, now, will all those people writing impassioned defenses of source protection and the journalists who protect them now write angry condemnations of Time? Will Howie Kurtz bash his bosses?