"surely it is unfair to treat 2 students differently?"
The thing is, EMA is related to course attendance and participation, and if a dependent receiving it did not attend or participate in learning, it is deemed that the money was not needed during that time, because logically speaking no learning took place (which is what the money's all about).
When parents choose to (or in some cases are forced to) use the state to support their children in whatever way, they have to agree to working within a well-needed system.
In terms of someone who can support their own kids, in this case through earning a reasonable wage (and declaring their income!), well they as a consequence are not part of the same system. A parent fully supporting their child can have their own systems in place. I guess one of the things self-supporting parents gain over those who rely on the state is 'control' and choice - in many areas of life. Although I agree, who really has such money to hand out to their kids.
I'd expect that if your child is not participating in or attending a course, you would consider whether you should ask for the money you handed out for this to be returned or owed to you.
I would expect most parents supporting their children in education without the state's help, would not just sit back and ignore it if their kids were simply not bothering. If that was the case though, well that isn't fair either, because, their kids are not being given good guidance or support, and I really do feel youngsters need this and not just money. Something they'll appreciate later on in life; at least the state attempts to motivate children to take part. I think the unfairness is more related to kids from parents who are on incomes that mean they get no state support, but are only just about managing (like me!). But logically speaking, even that's fine, if I gave £30 to my child for attending a course and participating, and he/she didn't, I'd want it back. If I gave nothing, there's no impact. It's not actually about punishment, it's about not giving something for nothing.
If you look at all other areas in peoples' lives, you could compare those and say they're unfair too.
I've no idea if this helps at all!