Yes we have loads of European figures missing as you know - that probably accounts for ~10-15m units. PSN will account for another 5m units.
The rest will be units in the channel - it's not unusual for a current platform to have 20-25m units in the channel this time of year, with 50,000 stores worldwide selling games that only works out to 400 games per store (+ warehouses etc) per platform.
You'll find a similar situation with Wii and Xbox360 - we have total software about 30-40m lower than shipments for both, DS and PSP lower still since it is mainly pre 2007 figures in Europe that we are lacking and obviously these came out back in 2004/5.
Nintendo give a breakdown per region so you can compare that pretty quickly and see how much is from units in channel and how much is from sales we have missing (in Europe).
Also if you use the new worldtotals page you count all the games which we have an LTD figure but don't track weekly.