It's pretty simple: Post-oak is the Central TX wood with the most mellow flavor, and is readily available around the area. It produces a great flavor and aroma, and everyone wants to recreate it in their BBQ joint and in their backyard. But nothing is saying you have to.
Cut it with pecan, live oak, hickory and maybe a little mesquite and you can still make some badass BBQ. I learned to BBQ on an 80 acre ranch with post oak, live oak and mesquite on it, and that's the wood we'd use. I'd put the flavors you get from mixing those up beside your typical post-oak only you get in central TX.
Pinkerton's (in Houston and San Antonio) does a mix of post and mesquite, I believe. His brisket is one of the best I've had here. Don't be scared of mesquite, just respect it.