This restraint may partly reflect Microsoft's market strategy--after all, Microsoft beat Apple partly because Apple did practice vertical foreclosure, and as a result inhibited the development of complementary software (although the main problem was Apple's persistent belief, despite all the evidence to the contrary, that everyone would be willing to pay a premium price for a niftier machine).
Apple believed people would pay more money for fancier machine, even though evidence said otherwise.
Apple bested Microsoft and were correct in believing people would be willing to pay more money for a fancy machine.