I think that, perhaps, there is a level of misperception going both ways in terms of your view of CR. I've watched it since it started, and Matt & Co. don't treat a natural 20 with any more effect than is usually the case with many/most homebrews-meet-game rules (that is, Matt allows for a 20 to be a "crit" for skill/ability checks -- having something extra happen, when/where appropriate -- but he doesn't in any way, shape or form treat it as "magically warping reality" -- he has on a number of occasions checked against the PC's ability/proficiency mods to the 20 to see...