what's is the purpose of saying "I need Perl 5.xx or higher"?

That way we can specify a minimum release.

I suggested that particular syntax because it uses existing syntax rather than inventing new, so versions up to and including 5.14 don't barf.

I appreciate that the meaning of the use will change to mean emulate a particular release, I'm querying whether that will be always feasible. If a feature needs to be changed, then being able to support both new and old could make the code even more complex, and might not always be possible every time. I think Jesse said as much in his talk, at least that was the impression I got.