It is rather silly from a game-play point of view - one would expect that higher level loot is better protected. But, from the other side of the argument is the view that, realistically, not every master chest will be used to hold good stuff. Im guessing that that is the reasoning behind the random loot - since a level 1 character can open a master lock, it could be 'game breaking' to always have high level loot in there. (i use the term 'game-breaking' loosely because in my opinion the whole concept of lockpicking is broken in Skyrim - the lockpicking skill tree is not needed to lockpick any chest).
If i had designed it, i would have had a higher percent of high level stuff in master chests, but made it harder to open them. In Morrowind, you could only open a level 100 lock if your Lockpicking skill was high enough. It was still possible to open the chests if you were lucky (either with a key, or spell, or potion to increase skills ) but it seemed more likely that better loot was inside. Also, another important point is that a medium level lock was easy to pick with a high skill, but hard to pick with a low skill. In Skyrim, a higher lockpicking skill actually means nothing (apart from allowing you to pick a set of, IMO, quite worthless perks). I can open a master chest at level 1 lockpicking - as i said before, that ( to me ) is broken; there is nothing to make me want to practice lockpicking.
(I know i've started talking about Morrowind - its not because of 'nostalgia', its simply because i think that it had a better way of doing it.)

Just my opinion though, of course.
