Define "average penetration."
Doofus is correct in sense. That is, Nevada. In 2006, AC had 3 6-deck games. The Taj cut off 1.5, the Plaza cut off 2.0 and the Borgata fluctuated from 1.0 to 2.0. As of 2007, the Taj no longer has a 6-deck game, Plaza is the same and Borgata cuts off 2.0 to 2.5 decks. Thus, 1.5 is no longer the average for New Jersey--2.0 is. 1.5 still seems to be the average in Nevada.
As side-note: Belgium is only 10 to 15% penetration and the Netherlands is completely CSM (5-deck).