Apple could put out a terd and market it as revolutionary and the sheep would still buy it lol so saying about it selling doesn't mean much.
I highly doubt Apple could put out that bad of a product and expect it to sell.
Sure the 4S wasn't what a lot of people were expecting, but it was an enormous upgrade from those users coming off the two year contracts they signed with the 3GS.
Secondly, even if that was true, every product Apple has put out so far is at the top of market, except for their laptops and desktop computers.
But even those have had distinct advantages over PC's and pretty much rule the music, photography, and movie industry.
I was also informed the other day that they were popular in certain segments of scientific research. The National Institutes of Health is the third largest Apple network in the world and still is.
So even if they could put out a bad product and make it sell good, they are doing a hell of a job keeping up with the competition so far.
Also that still doesn't change the fact that you wouldn't be able to tell the difference between Retina and 720p. Except for, of course, watching videos.