I came to say that too. If anything, it keeps decreasing - the first app-capable iOS devices had no app store, and the barrier to entry for programming on either system keeps dropping (the SDKs and even the IDEs are free, for instance). The only claim I can see is the emergence of the OSX App Store - big shocker there, given the success on iOS - but that hasn't resulted in a lockdown of regular installs, and I doubt it will.
As to the XCode-is-required claim, that's been false for a very long time - their GCC is open source, and has been for years. It has only recently become easy though, I'll grant that.
Apple clearly sees iOS and its locked-down environment as the future and Mac OS X as the past. Given that, we can conclude that the overall openness of Apple's offerings will decrease as they focus their efforts on iOS.
Xcode is for-pay now, while it was free earlier.
Apple keeps breaking SIMBL.
Debuggers now need to be signed by Apple or self-signed; either way, it's a pain.
>Apple clearly sees iOS and its locked-down environment as the future and Mac OS X as the past
Citation needed? Or are you pulling that from OSX getting a dose of iOS UI? The existence of the app store is merely a sign that they make money from the iOS one, and wish to make more money.
SIMBL is a hack used to load hacks (a fantastically useful one, don't get me wrong there). Its very nature is fragile, and Apple has zero responsibility to make sure it continues to work.
As to the XCode-is-required claim, that's been false for a very long time - their GCC is open source, and has been for years. It has only recently become easy though, I'll grant that.