Pauli Olavi Ojala does a good job of making the case against upcoming Apple rules–similar to those already in place for iOS–which will greatly restrict the capabilities of OS X programs that are sold through the Mac App Store:
Need to access hardware using something else than USB, for example Thunderbolt, FireWire or Bluetooth? Tough luck. (Just because these interfaces are on your Mac doesn’t mean Apple wants anyone to use them via 3rd party software.)
Need to communicate with processes that your app didn’t directly start, or perhaps take screenshots? Not going to happen.
Maybe you’d like to read and write files in a known location on a network disk? Not possible, unless you pop up the Open/Save dialog for every file.
There are two reasons not to get too worked up over the new regulations. One is that software developers don’t have to use the App Store–and software distributed through other channels doesn’t have to hew to the new policies. The other is that the sandboxing that Apple is enforcing has real benefits. (The company may say that Macs “just work,” but its sandboxed OS-based products are far more reliable than a Mac or any other old-school PC.)
If Apple ever starts to make it difficult to avoid the Mac App Store, I’ll get alarmed. (I’m already worried about Microsoft’s apparent plans to permit distribution of new-style Windows 8 software only through its app store.) But as long as the App Store is avoidable, I think we’re okay. Think of buying non-App Store apps for your Mac as being like jailbreaking your computer–except you don’t actually have to jailbreak anything.