I dunno, it's almost not any different from saying that All OSes are completely insecure because they all allow people to DL and install programs.
Really, I'm serious. Even if every single other possible hole was fixed in every OS and every app, if you continue to let people individually develop, distribute and DL apps, you will have a GAPING unfixable vulnerabilities (As the mobile app market is finding out in spades right now).
This "trick" isn't really a trick at all, you still need to get the user to do something to "install" the file to start with, the difference between that and getting them to launch any random executable is pretty much nothing.