Could it be that it was Android that hurt Blackberry and Nokia more than the iPhone did? Low end Android phones definitely replaced a lot of Symbian phones in the marketplace. It would certainly explain the timing of the change.
>The idea that Apple is vulnerable to the low end is a relic of an idea.
Not seeing how this follows from the data and analysis and seems to be a rather bold claim. There is a real chance of smartphones getting commodotized and it has already happened to a certain extent in China and India, where local OEMs are calling the shots.
The reason it's not happening in the US to the same extent is that the carriers hide the true cost of the flagship phones into two year data contracts, unlike, say PCs. However, the contract free prepaid market is growing at a record pace [1] and we may see a real change in the marketplace if the trend continues. Is the upgrade to S4 or the 5s from the S3 or 4S worth $500?
[1] http://www.fiercewireless.com/story/npd-one-third-us-smartph...