Well, except that didn't stop Apple from offering iBooks, Find my iPhone, iTunes U, Apple Store, Remote, Find My Friends, iTunes Movie Trailers, AirPort Utility, and Cards apps for free…
I believe Apple uses different income recognition rules for iOS devices than they do for OS X devices, and that may account for the difference here.
(This used to be the case with QuickTime: the basic stuff was free, but if you wanted additional codecs you had to upgrade to QuickTime Pro, for real money -- but it wasn't all going into Apple's pocket: it was simply that if they'd bundled all the codecs with the basic application they'd have been liable for extra royalties.)