I have not read much in regards to WHY this exact same bug was also found in OSX. Can anyone shed some light on this? Do they use the same code stack for iOS a

I have not read much in regards to WHY this exact same bug was also found in OSX. Can anyone shed some light on this? Do they use the same code stack for iOS and OSX? This seems weird to me - even though parts of code could be used in both operating systems, I would imagine separate teams would be on iOS and OSX, each reviewing code bases on their own, running unit tests and whatnot. Still, this major flaw has been present for 2.5(?) years - all the more reason for paranoia about its presence. Add to this, why wait so long with the OSX update? A security issue THIS serious MUST be patched instantly and rolled out as an individual/separate update as soon as possible, even if that means pushing back OSX 10.9.2. Or did they need some time to introduce a new flaw somewhere? o_O