As strange as it might sound, the method used for such lights is related to the way the whole airport is made, and the top priority for KIAH was to create a very large airport that would never crash or OOMs.
This was the result of all the UNFAIR criticism we received when CYVR (which I think is our best looking scenery BY FAR) was wrongly accused of causing OOM, when its only fault was it was located in an area that was already very memory consuming, with other 3rd party addons taking most of it, and users flying there with memory-hungry airplanes too.
After we PROVED (with many screenshots and memory tests, indicating the *airplanes* used were the most memory-consuming items, not CYVR ), this raised some awarness on the FSX community to be more careful how much stuff you install and the VAS limitations. And the memory savings offered by using DX10, which some popular addons made to allow the use of DX10 more feasable. It all started with the unfair criticism we received for CYVR.
So, we designed KIAH, the next scenery, with the utomst care on memory saving, trying to make the most RELIABLE scenery we ever made. And this clearly succeeded, since you can see for yourself, that KIAH has the LEAST amount of support issues of all the product we made.
Of course, since there's no free lunch with anything, and especially with the limited resources offered by 32 bit, KIAH might not look as spectacular as either KLAX or CYVR, both because it has been designed with reliability in mind, but also because the REAL airport is NOT as nice (nor lives in a comparably nice area) as the others so, instead of being unfairly criticised for wasting memory, some mistakenly though KIAH as being of a "lesser" quality compared to some previous products, when in fact it achieved exactly what we were set up to do with it.
Note that, when we made KIAH, there was no FSX:Steam (which frees lots of VAS compared to FSX) and P3D was V2, which instead *consume* more VAS than FSX so, the decision to made KIAH the way it was made, was correct considering the environment it would run under at the time it was designed and released.
It's POSSIBLE that, now that we have FSX:Steam and P3D V3, that has been greatly optimized in VAS comsumption, we might upgrade something made in the past to make use of that additional memory.