I don't have any Oreos to check ('cuz of their being chocolate) but if memory serves me they're either 3 or 4 rows in a package. Of course, it's been a good 15 years since I bought any, so...yah, the memory's not much help.

But when I was growing up, when I was allowed a snack, three cookies was always the number I was allowed. So that one doesn't seem as odd to me as most serving sizes do.