[ShinzonRemus]

What about managers and C-level people in multiple companies? I understand that these developers were fired due to performance issues, and that's ok (sort of*). However, this article implies that doing two jobs is "bad" for workers. If so, it should be the same for people in the upper-level of the company, right?

No, because (at least IMHO) it's not wrong per-se. It's wrong when (and if) it creates some performance problem.

* IMHO that's not OK for a reason: if the company cares about employees, it should understand the reason behind low performances and, if possible, help them. Often we hear that the "company is like a family": if your son will come back to school with a F, would you consider "firing" him out of the family?