Obviously, two people in 2 different DMA's are going to physically swap boxes from each others accounts, so that both people can get BOTH local channel DMA's in their homes.
And while yes it IS stacking & am NOT suggesting doing it, actually D* would probably get more $$$ from both subs; probably what they would do, is each sub would activate 1 or more extra boxes on their accounts, then swap them amongst each other. They would then have to remember to use the other subs receivers to view those other local channels. At minimum, D* is probably getting at least another $10/month they wouldn't be getting otherwise.
A little off topic - again while I am NOT condoning stacking, with the way both E* & D* keep jacking up their prices, I am seeing more subs (not clients of mine) that have figured this out & are resorting to this. (through NO help on my part - not exactly rocket science to figure it out, you know) With the economy in the toilet like it is, it's not all that surprising...