Penn is easily one of the most loathsome members of the liberal entertainment business, it's not surprising at all that he's a wife- beater.
The only good he's ever done was providing a lot of unintentional hilarity with his post- Katrina New Orleans boat debacle.
For that matter, I'm not surprised that Randy subtly admitted to being one himself. He lives in such a constant state of irrational anger and has such a consistent lack of morals, it sadly (For her) makes sense that he'd take some of his rage out on his wife/ girlfriend.