Skyline- it's hard to attribute the behavior you've described to solely the amount of mods someone has loaded. A poor choice of load order / bad mod install / fudged FNVedit usage could produce that. An inexperienced user with 100+ mods might be inclined to blame it on the number of mods they're using rather than their own error.
True but I'm just stating the case when one has too many .esp's / .esm's loaded. Even if they're blank .esp's, the end result will still be the same. There is a post on the Nexus regarding it and if you want me to find it, I'll source it.
Remember, there's a difference between # of mods and # of .esp's / .esm's. A re-texture mod doesn't count towards the # of mods usually. As well, highly modular mods are still one mod but take up a vast amount of .esp's /.esm if required, depending on what the user chooses. 'sides, most people that comment on how mod X doesn't work on their computer will have users A, B, C, etc... deny that happens and possibly attempt to resolve it. 95% of the time it works. The other 5%.. well you can guess.
Of course, I've only seen people mentioning this a few times in relation to the # of user-created errors that happen whenever I just play answerer on some threads on the Nexus. You can't forget though, some errors are caused by the authors themselves, which can't be ruled out. Human error happens; that's why other humans need to point them out.