There isn't a need to communicate it, it is just known to everyone that works in those professions.
I think there's more need to communicate it to people before they enter those professions.
In a 50hr week I expect to get about 20-25% more done than a 50hr week.
Yes, that's what people expect; the point is that they're nearly always wrong. I would happily bet good money that you won't get anywhere near 20-25% more done, although it's possible you'll get a small amount more done because, well, all of this kind of data is based on statistical averages and it's doubtful anyone has studied the exact job you do. But overall the evidence is clear: working more than 40 hours a week reduces efficiency to the point that the extra hours don't result in more work getting done across a range of jobs.
Yes, employers could try to abuse workers and then suffer poor productivity if they are pushed at 60-70hr weeks for months at a time with no end in site but a few weeks to ensure a project meets its deadlines is going to improve productivity in the short term.
Yes, that's true. Maybe my time in computer games has soured me but I simply don't trust employers to stick to that without well enforced legislation.