In my experience, early employees at startups don't usually just work from nine to five. They usually _do_ make large time sacrifices. I would say that early employees generally _are_ entitled to a fraction of the profits.
Who would join a company on an assumption that they have equity if it's not written into the contract?
B: Nevertheless, "fair market rate" typically includes gaining equity over time at a company. More equity the younger the company is and the more it is growing while you're working there. If you work for "fair market rate" at Microsoft, Google, Amazon, Facebook, etc. you get stock grants, stock options, the whole nine yards. If you work for "fair market rate" at an up and coming startup you'd expect to receive stock as well, and in comparatively larger chunks.
We can enter in the sympathy realm after this, but no one was entitled to anything. If they didn't like the job, or felt underpayed, they should've done what everyone else does: Try to find a comfortable solution with their company, and if that doesn't work, leave and find a better job.
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".