Obviously apple will gladly lock down, control, restrict, and regulate their users (and even their devs) when it serves their purpose. Just look at iOS. The entire platform is restricted from top to bottom.
For their iOS products, more locked down equals more safe. They're treating them more as appliances than as general purpose computers. For consumers this has some appeal: The risk of malware and trojan/virus like applications is effectively zero on iOS.
If there was a way to offer security without locking things down they'd probably do it, but I think that's a logical impossibility.
If you don't like that model you have a ridiculous number of alternatives, more so than in the PC space.
So this is less a case of Apple using DRM when it suits them and more a case of Apple using DRM when it suits the consumer. Running only trusted, signed applications is a limitation, but it's one that is not without benefits.