@ Veekie
A & B shouldn't apply to this discussion. They are, as you said, another kind of game issue.
D is
supposed to be taken into account for CR, though no actual formula is ever given.
C I'd agree with you, except: the point is, if a Gynosphinx manages to hit you with it's Symbol of Death, and you roll low / a 1, this has nothing to do with CR high or CR low, that is what the problem with IP is.
Monster manual creatures are generally speaking, weak. Optimized T4 would face practically no danger from a monstrous foe, barring specialist creatures that have a primary save-or-die or one sided environments.
This is the point of the IP argument. It would be easy enough to say "don't use these creatures", "don't have those creatures use that ability", or "modify / nerf the ability to work differently". Except that those are fixes that go beyond RAW, and the "IP debate" is a CO point. Thus is meant to follow RAW.
@ Phaedrus
umm... the point is that IP-proofing is a CO point. The idea is levels of statistical insignificance, and the concept of wondering if there is ever a way to fully safeguard yourself. In other words, can you survive the infinite? Which would be / require TO, like pun-pun.
@ all
Just in case my personal stance wasn't clear, what actually matters is the game.
"The most powerful character is the one you actually get to play."
All of this is just a CO thought exercise.
The only real point is what level of IP proofing is "required" for that particular games power level.
*ahem*
The Gentleman's Agreement