This is intentional. If Apple starts selling iPads as full fledged computers, who would buy macbooks anymore?
As a company you have to be the one making yourself obsolete all the time to innovate and survive, because if you don't, then other companies will.
Fear of cannibalizing existing profitable products with new ones, is what killed Nokia, Kodak, SGI, Blackberry, Philips, etc. leaving them as husks leapfrogged by more brash competitors.
If Apple are losing a sale, they want to lose it to themselves. I'm not sure they'd be worried about being unable to extract more money from the customer, that's an area in which they seem flush with ideas (perhaps, an iPad Ultra with encrusted diamond frame?)