I guess I could give you a few scenerios, it isn't hard to imagine. Too many login items. I've seen preference files become corrupted over time and I had to clean them out. I've seen people with a **** ton of widgets going that begin upon startup. Conflicts with permissions has been a solution for me before. I even found one that had a ridiculous amount of firefox extensions that caused the computer to lock up upon getting on the net.
Some of these are software related but I am stating them to say that there isn't an idiot proof OS. People will always find a way to bog their system down or infect themselves.
I think I've said all I am going to say. We can agree to disagree. I've stated my opinions on the matter for the casual user, and you have too. We have both made valid points and in the real world for the common user it probably doesn't matter at all as long as they can surf the web.

