I actually do make a decent bit more than my roommates, but I choose to live an extremely simple life for other benefits. If my rent was higher than it is now (to match my income), living there would not be worth it and I would get my own apartment without roommates, etc. It would also create trouble between us as I don't always find the benefit in just having them around for how great they are.
I can very well see how your situation works for you, but I do not agree that my setup is at all unfair.
As far as cleaning goes, none of my roommates have the income to constantly pay professionals... So that is why they can take a pick off the list as opposed to being assigned tasks.