Yeah, Apple did, and in the business world, this is called not knowing exactly and precisely how the market is going to react to your brand-new device (I've already opined on this previously).
There is no magic ball that tells Apple that they need precisely so much inventory of any given configuration (think of all the different color, size and memory combinations), so they estimate based on whatever metric they use (nobody outside of Apple actually knows, and Apple's not saying).
In fact, it's going to be even harder to speculate now, because prior to preorder, Apple announced that they would not announce their first weekend preorder numbers.
So, are they that stupid? Yes -- but no more than any other company or organization in this galaxy that knows you cannot possibly predict exactly how much of what you make will actually be consumed by the market.