Apple filed a patent on this Virtual SIM card in 2011. More info here: http://www.patentlyapple.com/patently-apple/2011/11/apple-in...

The linked article suggests it's a method to save space in the hardware design so the SIM is not user serviceable. However, it also forces you to only buy data service from Apple approved carriers. Notice in the screen shot from the OP's article that Cricket or any of the more affordable MVNO's are not available as options.

This change is just as much about control over where you spend your carrier dollars (and, possibly, Apple getting a kickback) as it is about saving space.