I see you are part of the "written word only" style of ethics. This is where you declare only those things prohibited by written law or contract to be unethical, and then grant inventive persons the status of geniuses when they find new ways by which to exploit you.
I am not, and despise exploitative use of law. I believe human behavior is so complex, that defining what is acceptable or not in paper for all the possible cases is borderline impossible. Written, clear laws have their place, as does human judgement.
That being said, it really seems clear in this case.
Compensation for work is one of the things defined at the beginning of a work relationship, comfortable for both parties. Minecraft was already big when anyone was hired, I assume that if any extra compensation besides salary was expected, it would be asked for when the work started. Disgruntlement seems a bit out of place, and seems to be used in the piece to adorn a non-story.
Plus, note that my course of action would be talking to your employer to try and find a solution that works, not just "suck it up".
