Airline pricing schemes

Who designs airfares and what's so special about Delhi?

I'm trying to book travel to India this summer and I need to go to both Delhi and to MAA (Chennai). I'm trying to book it so that I can fly OKC-MAA and then from DEL-OKC.  Indian carriers are nice enough to price one-way tickets exactly half the cost of a round-trip so I can be pretty flexible on when I do the MAA-DEL thing.

But booking a multi-city OKC-MAA, DEL-OKC trip is providing quite a lesson in airline pricing. It's cheaper to fly roundtrip OKC-MAA-OKC than OKC-DEL-OKC even if the stop-over is in Delhi! Something to do with competition and convenience, I suppose -- there are direct flights from DEL to several East coast cities but MAA is too far south for a direct flight. You have to change planes in Europe or in Delhi.

Now for the irrational: I can fly from DEL to MAA, then hop on a plane to OKC through DEL for cheaper than it takes for me to fly from DEL. In case you didn't quite catch that, the airlines will pay me to take a round-trip from DEL to MAA.

I ultimately ended up buying a ticket from Jaipur to OKC via Delhi. Instead of paying extra to fly out of Delhi, I'll pay a cab to take me to Jaipur, tour the city and then fly out.