What could be more "incredibly...stupid" than to not meet demand of a hot product when there are a plethora of competitors also vying for a share in the market?Seriously? You don't know why Apple can't magically manufacture enough units to meet initial launch demand? Leaving aside all the practical problems (component supply, overall production capacity of the manufacturer(s), massive amount of inventory sitting in boxes rather than being sold, initial production / process issues etc) they'd likely have to ramp up to a higher production level than they'd need going forward which is incredibly wasteful (not to mention stupid).
Oh and your example has a slight flaw: it assumes that your customers wouldn't pay more for one of the 10" iPads. Certainly your typical best buy employee would be more likely to try and push them to the more expensive purchase...
Someone mentioned it's not as big a launch as the iPhone 5 but surely that's to be expected. This is a new product after all and you just don't launch a new product with the sort of production volumes you do for an established product that dominates its market.
The new 10" iPad was also updated, and if Apple keeps an October cycle for it, the next redesign or new component(not in iPhone already) will cause a similar shortage, so the analogy stands.