This is interesting. I didn't realize 10 was such a common size.
I talked to a shoe salesman once, frustrated that they frequently didn't have my size, 6. He told me that they buy the shoes in lots and each lot has say, 12 shoes in it, with more of the larger sizes and only one or two size sixes because it's supposedly less common. And that's why they don't often have my size. I don't think it's that uncommon though. Frustrating.