I think non-technical people are easily distinguish between a 10 inch and 12 inch screen, but do not understand that resolution is also important. The Mini 10 (not the 10v!) has the option for a 1366x768 screen, while the Mini 12 has 1280x800 screen. Resolution-wide, the Mini 10 is "bigger."

Part of this confusion might be because of Dell's pricing. When I was looking earlier this summer, the Mini 12 cost more than the Mini 10 (with the high-resolution screen), despite having similar hardware specifications.