It's not a "requirement" if it's not actually required. I can guarantee you that if someone were to go into, say, silicon valley and find every single developer who got a job in a role which was advertised at some point using the word "rockstar" or "ninja" and then compared the average talent/skill of that pool of developers vs. developers as a whole there would not be much difference, if any.

Edit: I think I slightly misread your post, so you have my apologies.

It is much in the same vein as the silly "requirements" of x years in y, z years in w, etc. And a stack of degrees. Usually it's just a way to keep the walls high to weed out the truly unqualified.

No, I understand it can't be formally understood as a requirement - but that's how it's phrased. Hence my comparison with todays unrealistic "requirements".

Nah to me "rockstar ninja" it is just a marketing term. Sure it sounds great and may fill arenas of recruiters but I still can't quite define what such a person is.

Is it a good programmer who knows all the bits and bolts of a given language or an adaptable developer who can master concepts from another programming language? Will the ideal candidate write good code AND good tests?

It's just too vague... Simply doesn't rock my confusion.