[Swordmaker]

...execution of any executable from the buffer...

Oops, make that "Execution of any executable from the stack."

[Senator Bedfellow]

Unlike Windows, OS X does not permit execution of any executable from the buffer... so the most it can do is to crash Excel on a Mac....Oops, make that "Execution of any executable from the stack."

I'm sorry, but that's not even remotely true - you can smash the stack on OS X with a buffer overflow, just as you can on just about any other OS. Here's one example of same:

http://www.idefense.com/intelligence/vulnerabilities/display.php?id=239

Any OS written in any language that doesn't automate bounds checking at compile time or runtime, such as C/C++, is potentially vulnerable to this sort of thing. And that includes OS X - the only thing you can do is patch 'em as you find 'em, or rewrite the thing from the ground up in a language that is a bit more sensible about such things.