I think Preistidigitweeze has a good point - younger users are becoming more critical in how they can use their devices. But apart from that I think that Apple had a certain "air" to it because it was closely linked with "design" and being something special. Of course, if everybody has it, its not special anymore. This is as well (one of) the reasons why Apple was always expensive: It maximizes return and maintains the brand. By becoming cheaper, they could have sold even more, but they would not be "special" anymore. By now (or actually some time back already) I think they passed the point of sales that make them fully mainstream. This will in the mid-term hurt the brand, I think. Similar issue with Porsche: They price their cars not by manufacturing cost, but by branding objectives (and profit) - and even they are expanding too quickly for my taste. Even my neighbour could now be driving a Porsche (and yes, he would have an iPhone).
All the best,