Yep.

I would expect MIT's exams to be outright impossible for a mortal to pass.

University of Wisconsin's will be nearly impossible to pass even with concerted study.

Northern Illinois will be possible to pass with study.

and then there will be institutions whose certifications don't mean a whole lot. There's no question about that.

But MOST people will try to pass the impossible ones... because the payoff will be so much bigger. Only a few will pass though. I'm thinking the tests will be designed that way. I strongly suspect getting a degree from UMichigan, UWisconsin, UTexas, Berkeley, etc. will be MUCH easier if you just attend. But this is a good option for those who, for whatever reason, don't wish to do so.

Well, you can easily test your theory in some cases. Many of MIT's open courseware classes include the exams. Are they impossible for someone without any knowledge on the subjects? Pretty much, but if you follow the course content, they are passable.