Romney interrupted the president many times in the first debate and was praised for this as a show of aggressiveness, while the president was criticized for not responding. Biden interrupts Ryan (like Romney did to the president) and is criticized for being impolite, dismissive etc, and Ryan is praised for not responding, keeping his cool (like the president did vs Romney). It seems to me that the media coverage is highlighting these differences based on expectations that they set in advance of the debates, just like reality TV shows and scripted dramas set up expectations and then defy them. Everyone expects Obama/Biden to win this election, and the media just keeps the horse race interesting to cash in on advertising and eyeballs. JMO.