ETH-D is another scholarship aside from ESOP, but the budget mainly comes from the ETH-Departments. So it depends on the department you are applying to if they are rich, they can have more than 1 scholar under the ETH-D It's also said to have a "partial" scholarship which just means that the allowance given is slightly less than the ESOP, but I spoke to a former ETH-D (it was called MSP before) Scholar and he said it was still enough to live off of that you don't need to shell out money.
I've heard about instances like that wherein people had to take additional courses. To be honest, for me, I think it's not the worst thing to do considering ETH is still very selective of its students. As for my program, they are just requiring some credits that are similar to their BS Mechanical Engineering or BS Electrical Engineering and Information Technology. It's just really confusing because my degree (Manufacturing Engineering) is not that known anywhere really ???