I'm not sure why this poll is a surprise to anyone. Perry usually get something like 55% of the vote even on his best elections with the most favorable GOP environment. I expect he'd get 54-55% or so in a general election with Obama getting 44-45%.
It's because the conservatives expect Texas to always remain a safe R state. The idea that the margin would be close in the President's reelection makes the conservatives cringe because they realize Texas could change for them in the next few cycles and it would be a problem for the GOP