From the
article (which is heavy on number crunching):
At a macro level, there were 7,359,621 votes cast in the 2004 Presidential election in Texas, and 8,007,961 votes cast in 2008, for an increase of 648,340. Note that in all cases all I'm considering is the sum of the Republican and Democratic votes - third parties and write-ins are not counted. Bush/Cheney got 4,526,917 votes, while McCain/Palin got 4,479,328, for a decline of 47,589. Kerry/Edwards received 2,832,704 votes and Obama/Biden received 3,528,633, for an increase of 695,929.
I've been preaching this for years. It's all demographics.