I don't think that Apple is protecting the iPod touch but they are definitely are protecting iPhone margins. ThiPod touch is selling less year over year.
Apple's growth is starting to decrease. They're no longer getting 100% year over year growth for iOS devices. Even Gruber assumed the 3GS would be available in poorer countries but it hasn't.
Apple is going to have to eventually find growth beyond the iPhone and iPad unless they're willing to lose subsidies for the iPhone or take less margins for the iPad to increase growth.
I don't see why Apple has to reduce the margins on the iPad or the iPhone when they can't keep up with demand. They sold 5 million iPhone 5s the first weekend and they could have sold a lot more if they could have made more.
The growth trajectory of the iPad is unprecedented--100 million in 2.5 years.
Apple is smart about not getting into the situation of having to reduce margins on products--they use economies of scale to reduce costs.
Growth, or lack thereof, affects stock value which also can affect future talent employment and current employees. While the iPad may have future growth ahead, many will not pay the unsubsidized price for the iPhone, which is where most of Apple's current valuation lies.
Rumor has it that Apple is only getting ~25% margin on the iPad mini which is unprecedented.
Apple's growth is starting to decrease. They're no longer getting 100% year over year growth for iOS devices. Even Gruber assumed the 3GS would be available in poorer countries but it hasn't.
Apple is going to have to eventually find growth beyond the iPhone and iPad unless they're willing to lose subsidies for the iPhone or take less margins for the iPad to increase growth.