Startups are sometimes spread quite afar, Mojang was in Stockholm, and are not always likely to survive. While Notch was "rolling in the dough" there was no guarantee that it would continue indefinitely.
That risk is why employees, especially early employees, feel like they should get some equity. It's a trade-off: they are accepting a percentage chance that they are joining a company that could fail, but there's also a chance it could be wildly successful. The difference between equity and wage represents an assessment of risk and riskiness. And, of course, offering lower wages and higher equity shares creates positive incentives for employees to go above-and-beyond and ensure that the company is not just a mild success, but a multi-billion-dollar-buyout success. This is opposed to the perverse incentive that wage-only compensation creates, where a buyout potentially means losing your job. After all, if you weren't valuable enough to deserve equity, you may not be the talent the new company was seeking to acqui-hire.
In this case, it is almost certainly the case that any Mojang employee would have better off foregoing all wages in exchange for a small amount of ownership.
With hindsight biases, I suspect every Mojang employee would say they'd be willing to give up some wages for some equity. But before the acquisition, it was nowhere near clear that the company was worth $2.5 billion, so I wonder how many employees might still be willing to take that offer.
So, like I said, trade-offs. I think the tone at the end of your post represents how a lot of founders might look at it, and I realize it's hypothetical. But stepping back from the situation, there are complicated incentives involved in wage and equity compensation, and balancing those as a founder or an employee can be difficult.