Forgot to answer your question. The reason is, ultimately, you have no problem flying out of IAH. In fact, you probably plan to. It's like Chase readily admits on page 1 of this thread. SWA is going to end up going to DFW. Even with all the decades of WA drama and consternation, SWA will end up going to DFW. Houston doesn't have to wonder what your plan is. You intend to skirmish from a safe distance with the IAH carriers, assail IAH as ridiculously expensive, and ultimately wreck the airport financially and contribute to the bankruptsy of the predominant carrier. Then move in when you can get the whole thing for cents on the dollar.
I think that you are being a tad over-dramatic. SW can only do so much with 737's, UCAL has a lot more reach, seats and airplanes of all types. SW will probably make the total market bigger rather than stealing a lot of business from UCAL. CAL has done very well competing against SW in Houston for a long time. The 737 has been a key to the success of SW but it also serves as a constraint for SW.