Golly gee whiz, Bush had to cancel his photo-op-- I mean, uh, check-up on Hurricane Rita preparations in San Antonio. Reasons? With the hurricane moving furthur east, disaster prep teams had to move that direction as well to stay closer to the storm. Plus, it was sunny in San Antonio and Bush wouldn't have looked like he was travelling into the storm.
http://www.nytimes.com/2005/09/24/national/nationalspecial/24bush.html
Therefore, Bush went straight to Colorado Springs. Ridin' the storm out in a mountain. There was also the possiblity that had he come to San Antonio, he would've interfered with the efforts to move the disaster prep out of San Antonio towards the east.