Because Apple is built as a harware company. They couldn't sell hardware when dell sells bare bones for $200-$500 less. Give a little time to transition, as the "biggest" hurdle to getting OS X on intel machines gets accomplished(when all major OS X apps are written/compiled for intell).
Once that is done, branching out to the rest of the hardware becames A LOT easier for Apple.
if they could sell their $100 OS to WAY more people what is the loss? IF you can keep your Apple hardware faster and more reliable as compared to the cheaper PC alternative, people will still buy it.