I think one of the things is that most Texas BBQ is not done over mesquite, it is done over post oak, something that is hard to come by, most everywhere else. It is a hard, dense wood, that burns evenly and moderately for a long time. Similar to the Coast Live Oak we have in California in terms that they are both live oaks from the Red Oak type, they have similar characters.
Again, I think the term BBQ has become over specialized in some circles and over generalized in others. I am of the belief that Santa Maria BBQ, as it was originally, is absolutely BBQ, and that burgers and hot dogs are not, they are grilling. Further, I would say that if what you think Santa Maria BBQ is, is the cooking of tri-tip over a hot fire for 5 to 10 minutes a side, you are then grilling and not doing real Santa Maria BBQ, you are doing Sunset Magazine/Bobby Flay/Steve Raichlen/Food Network interpretations.
I go further than you do Bo, but, I think your reevaluation is getting close to spot on.