It's the semantics that drive me crazy. Try ordering a small pizza at Dominos. They only have medium and large, which are as large as a traditional small and medium, respectively, but priced like a traditional medium and large (I only order Dominos with a coupon).
No, a medium Domino's pizza is and has always been 12 inches.
Large is 14 inches.
The small was a 10 inch pizza, but they don't carry it anymore.
I haven't read through all of the replies, but Domino's does have a "Personal Size" pizza. It's too cheap for them to deliver, but if you pick it up, it's just fine.