Hmm, really? I have caught quite a few musky in the campground that I go to every summer. Never got a huge one, but 10-15 pounders aren't that rare. The lake is infested with northerns, musky, and tiger musky, and you catch some if you put in the time. I usually get them on live bait, but you only get a musky once about every 10-20 fish, so they are definitely rarer than others, but not "the fish of 10,000 casts," at least not there.
I never knew how difficult they were supposed to be to catch until I saw this thread and looked them up. Maybe the concentration in this lake is just much higher than in others, but I never considered them really difficult to catch. I have only caught one in a different place once, so maybe I just found musky heaven or something.