Perhaps there is more violence, but did they ever stop and analyse what kind?
Fact is - written words probably aren't as instantly graphic to children as television is. Most if not all television programs are thought out in a way that attracts the viewer to what they're watching, and tries to hold their interest. The violence displayed will be easier to associate with real life than a nursery rhyme could be.
The end result? Nursery rhymes are no doubt safer to teach to children than sitting them infront of some soap where a man hits a woman ever could be. Sure - Jack my bump his head, Humpty Dumpty may break his. But it's a little bit different from Shaun trying to run over Sarah with his BMW, then getting out and beating her.. or Katey taking drugs then slapping her friend because she's lost control of her mind...