They're eating the seed corn, but they don't really care since they won't feel the effect for 15 years or more. I personally don't care much either, unless they manage to fully legislate their locked boxes as the only option... which they are trying to do whenever we aren't looking, by the way, the most recent being with Microsoft locking out other OSes on their ARM boxes.

Yes. It's clear that Apple considers the relative openness of Macs a defect which they're only keeping around for backwards compatibility.

unless they manage to fully legislate their locked boxes as the only option... which they are trying to do whenever we aren't looking

Or even when we are. Apple has been quite open about their desire to destroy Android with IP lawsuits, which would leave no significant mobile platform where you can legally run software of your choice. And I won't be at all surprised if the next version of OS X removes root access and the ability to run unsigned apps. (Neither of which you actually need in order to develop software for the app store; your test apps can be signed with a machine-specific key).

That said, I'm still getting the retina MBP as an upgrade from my 2006 model. AFAIK it still supports booting Linux if OS X becomes too user-hostile. It would be nice if every other PC manufacturer hadn't spent the last 5 years making their laptop displays worse, but oh well.

This is not remotely clear. Do you really think Apple wants the App store to dry up because they are the only people left who can develop for it? The Apps make the app store and they know this.