You notice the video execution of Mrs. Hassan that Al Jazerra has is not going to be broadcast. I mean, why show the true face of the fascist putting a bullet in the head of a helpless innocent woman. It just doesn't help the cause.
The reason it's no longer news is that it never was news in the first place, in the opinion of the "world press." The first couple of beheadings may have had a bit of sensation value, and it may have been perceived that they would harm the US cause by making us look powerless to stop them, so they were broadcast. Since then - silence.
Once upon a time, having a middle aged lady who was, furthermore, a CARE worker married to an Iraqui - and had even converted to Islam from the Catholic Church - might have been news. But that might make the Islamics look bad, so the press politely averts its eyes.