One third of Apple's U.S. sales in 2013 were to Americans making more than $100,000 a year, and of that group, Apple's share was 65%, according to NPD (which did not provide a spreadsheet supporting that number).

The bad news is that the cream of the U.S. market is also the segment that is growing most slowly – only 4% year over year according to NPD.

The fastest growing segment – people making under $30,000 a year – grew at 42% a year, double the industry rate. Only 20% iPhone sales went to that segment of the market, compared with 35% for Samsung.

Philip Elmer-DeWitt | Fortune

Selling phones or more accurately, selling a truckload of phones specifically to those under $30K means selling a phone with next to zero margins, and Tim Cook has made it clear that Apple doesn't give a lick about doing that:

“We’re not in the junk business.” The upper end of the industry justifies its higher prices with greater value. “There’s a segment of the market that really wants a product that does a lot for them, and I want to compete like crazy for those customers,” he says. “I’m not going to lose sleep over that other market, because it’s just not who we are.

Tim Cook interviewed by Bloomberg Businessweek