We have to keep in mind that the world economy has not fully recovered. Trading volume on a global scale is about half of what it was in 2007. The Dow is ONLY making new highs in dollar yet. The low volume is actually bullish from the standpoint it is not OVERBOUGHT. We will see volume pick up sharply only when it makes new highs in Euros.
Most still question the rally. That is also good for the long-term. This invites people to keep trying to sell the high and get stopped out taking the market higher. So do not worry about the low volume yet. We have not broken out INTERNATIONALLY as yet in real global terms.