Is one enough?

During Obama's speech about health care this past wednesday, Republican Joe Wilson shocked everyone when he yelled "You lie!" in the middle of Obama's statement about whether the plan would cover illegal immigrants. Telling the president that he is lying in front of the entire nation watching the broadcast on TV is bold, and probably pretty irrational. Almost immediately after the speech, Wilson issued a statement apologizing for his actions and he called the White House that evening as well; Obama accepted his apology saying Wilson "apologized quickly and unequivocally, and I'm appreciative of that." Although Wilson said "sorry" directly after the speech he refuses to say it again. As of late Sunday afternoon he told CNN that he will not apologize again for yelling out.

This is what surprised me. It is an unspoken rule in American culture that you don't call someone a liar to their face (especially the President himself), but it is a whole other thing to make one simple apology and then refuse to do it again, as he is doing right now. The House Democrats want him to apologize on the House floor this week, and plan to censure him if he does not. The fact that he refuses to make one more simple apology surprises me because he has already put out a statement and made his direct apology, so why not one more? It makes me wonder...

Was Wilson truly sorry about what he said or did he only apologize because he knew it was the right thing to do? Is saying sorry once enough or should he be more willing to express his apologies to other people (such as the House Democrats)? Is this true in all cases or just this one?