This is about a moral and ethical choice. Yes, burning a source is a very big deal, but why would they protect a liar? They're reading the comments here, and half my posters think Zengerle made this up on his own. Talk about a hanging curve ball. Frank Foer knows he's gonna face this again, and his refusal to do the right thing now is going to haunt him and TNR. Zengerle's credibility and a $1 will get you a dirty water dog near Central Park. But it won't get you a credible story.
If TNR thinks their pathetic, cowardly apology is acceptable, that is their choice. But they will be renminded of that choice many times in the future, by many different people, for many different reasons. Hiding behind a liar is a short term solution with a long term consequence.
A frequent complaint about bloggers is that because no one hires us there's no accountability, but I rarely see much accountability in journalism. People tend to get fired for relative stupid and inconsequential stuff, while the larger sins and sinners just sit there festering. I'd like to think the Times couldn't get away with their bullshit Whitewater reporting now, but 14 or so years later we're still waiting for them to print that "correction."
Personally I was astonished by the movie Shattered Glass and TNR's response to it. They were promoting the damn thing, and they were right to. Somehow it made them look good! Everyone managed to be a bit of a hero except for Glass himself. No one else was responsible.