Disney should really adjust the secondary parks with secondary admission fees. It is not fair to charge MK prices at the other parks, with only a fraction of the rides.
One day tickets do cost more for the MK.
But as far as multi-day and hoppers go, they are already
heavily discounted as it is, so that's sort of their way of subsidizing MK admission by charging an equal price for all parks on all multi-day tickets. Starting with at four day ticket @ $305, it's only $10 for each additional day you add. That's it. $10 for day 5, $10 for day 6, $10 for day 7, all the way up to day 10 (4 days is $305, 10 days is $365). Sure, it's their way of encouraging longer stays at the hotels, but it's hard to turn down $10/day for any park, especially for someone like me who doesn't go that often. 1 day at each park leaves me feeling terribly rushed. Maybe the Studios is currently exempt from that, but generally speaking, I like to experience the parks at a very casual pace, so 2-3 days is necessary for each one (again, Studios notwithstanding until Star Wars and Toy Story and whatever else are finished).
But really it's no different than an all you can eat buffet. You can go in and choose to eat the expensive menu items (Magic Kingdom), or you can just fill up on something else (the other parks). Regardless of what you eat, you still pay one price. The MK being the same price as the other parks is really no different than what happens inside an individual park when it comes to choosing what to do. Once you're in the park, you could ride all e-tickets, or you could spread it around, or you could ride nothing at all. No matter what you do, though, the price for admission doesn't change.
It doesn't really matter to me what the breakdown is in cost per ticket or that MK is a better value for a use of a ticket. I see it as an overall budget, and from there, I choose how I want to distribute the time I've purchased.