you're assuming that there's such a thing as "C". there isn't. what does exist, or rather, do exist are several different flavours of C, some defined by standards, some (most of them) defined by actual implementations of a given compiler. you see, there's a reason that gcc 4.6 as of today is still a masked package in gentoo for example. if the concept of a single C specification existed and everything was written to that specification, this situation would not exist, but it does. IOW, having a new flavour defined by PaX plugins is nothing out of the ordinary, it's the norm in fact.
now obviously not all flavours of C are created equal, so one has to carefully evaluate what's worth using and what isn't. for the PaX flavours the defining goal is always something to do with "make the generated code more secure, even if the original source code wasn't written with security in mind". whether it's something you or anyone else values is of course not up to me to decide, but i did decide that it was worth for me (and many others) to pursue this route.
as for bugreports, we've always handled PaX/grsec bugreports ourselves and directed users upstream only when we could determine that the given problem existed there as well.