Forty percent of the people in the U.S. read one book or less last year.
So that means MOST people (60%) read more then one book.
Even if only 20% of the population reads that group is bigger than the group of people who use Macs and Jobs is happy to sell computers to that small minority. I'm sure that if Jobs thought he could sell a book reader to 5% of the US population he'd jump at the chance. his goal with the iPhone was to sell one to only a small percentage of the population.
Also most people buy low-end, cheap PCs. If Apple follows the bulk of the consumer market why don't they offer $399 Macs?
Apple has always "cherry picked" the top of the market leaving the mid and low end to others.