They might be doing this because there is not a large enough venue available. I think I posted in the other thread that they played Columbus, NE in the summer of 2003, and yes, it was at the municipal airport.
The "backdrop" for the stage was one of the hangars, and there was a decent sized chunk of runway roped off for the audience. An especially nice touch was the beer tents

They drew about 4,000, and there's just nowhere in Columbus (small town that it is) to handle that kind of crowd.
Several kids from my school went to the show and really enjoyed it. Parents around here were a lot more receptive to letting their younger teens go to a show 30 miles away in a small town versus 2 hours away in a city like Omaha. For many, it was their first concert. Listening to how excited they were as they raved about the concert afterwards was the best. For me personally, that was more impressive than if Styx would've sold out the largest venue in the state!
The other bonus at this show was general admission. All the Styx shows I've seen in Lincoln and Omaha have had assigned seating and it's generally harder to move around freely, which I prefer to do.
All in all, it ranks right up there with some of the best shows I've been to.