It was more the walled-garden approach Apple took throughout the 90s that I was referring to. The steps they took to ensure that they were the only ones who produced computers capable of running Mac OS -- moving critical bits of the OS to on-board ROMs; applying government pressure when necessary to prevent the manufacture of early Mac clones which used reverse-engineered ROMs; later destroying the legitimate Mac clone market -- are eerily similar, albeit technically inferior, to the things they're doing today to prevent people from running OS X on unauthorized hardware and unapproved apps on Apple devices.

Apple already contends that OS X can't legally run on generic PC hardware, and has already taken x86 Mac cloners to court over this and won, so they know they've got the law on their side when it comes to control of their OS, where it can run, and what can run it.

The next logical step is to take control of what can run on it. With the recent OS X "virus" scare, the issue has become all the more urgent, as the public's perception of its security has been damaged and a signed-app "solution" seems like the easiest way to restore confidence in it.

As far as requiring signed code goes, though, their other devices already all require it, so I'm assuming, based on their moves so far, that it isn't far off on the laptop/desktop end. That it's an option (on by default) in 10.8 makes me think that, one day, the option to run unsigned code in OS X will disappear entirely.