Who cares if 30,000 programs are available for Windows, if the five you want most are available only on the Mac?
I don’t even care if they’re Mac-only, so long as they play nicely with the other children. How many programs do you use in a given day? Five? Ten? Anywhere near a hundred? Or a thousand?
30,000 programs is about as useful as the plethora of choices in the breakfast food aisle: demand creation, to make you buy stuff you wouldn’t otherwise bother with, and brand dilution, as more varieties of the products you like appear on the market, each more like a competing product than the one(s) they share a brand name with.