A very smart man a while back proposed that any given thing has two kinds of value: use value and exchange value. One does not necessarily overlap with the other, yet both can totally capture a things "value" depending on where you start.

If something has value of its own, then it will be purchased regardless of whether other unrelated products are or aren't purchased.

Thus, in order for people who don't find iPhones particularly valuable to contribute zero market share to the independent market for phone software, it can only be the case that phone software has no value.