http://www.youtube.com/watch?v=1U8ApfnjPsg
He talks mostly about the troops and economy but he did mention Christmas. Very politicized unlike his ramadan message.
That is from 2008.
Actually you linked his 2008 message. Here is this years WH message for Christmas. Again I think its mainly for the troops.
They even show hand-painted ornaments on the tree...except for the Mao ornament of course.