Southern Democrats were felt to be more moderate, so they were more likely to be nominated or elected than Northern Democrats.
The other part of the equation is the Bush family. In Massachusetts-born, Connecticut-educated Texan George H.W. Bush, the different parts of his heritage -- North and South, East and West -- cancelled out, leaving him sort of a neutral or generic American, or at least that was the hope. Something of that legacy carried over for his son, who was a truer Texan than the father.
But would a really Southern Republican have an inside track on the nomination or election? Would Hailey Barbour have had a good chance at winning? I don't think so. Maybe Fred Thompson would have, because he was Hollywood as well as Tennessee and the two cancelled out (and because Tennessee isn't Deep South).
Perry probably does stand a very good chance at winning the nomination. What could louse up his career at some point is that Texans (in the eyes of many non-Texans) don't know when to quit with the Texanism. The time comes when voters want Texanness. But Texans provide more of it than a lot of the rest of the country can bear.
True. I think Perry can be Cosmopolitan enough for the crowd. Another thing to factor in are all the northerners/midwesterners/westerners who have fled to the south (in particular TX) for jobs and lower taxes (maybe they'll email the folks who stayed behind and tell them to vote for the TX guy).