It seems that "great" developer is somewhat a synonym for "public" developer. I'm not sure how companies would just "know" someone is "great" otherwise. And yes, not all publicly known developers are necessarily great (or even good), but I'm not sure how one would recognize a 'great' developer without that person also having some degree of publicness to them.
And yet, I've known more than a handful of developers who are really solid, great people to work with, and I'd like to work with again. None of them have ever blogged, podcasting, presented at conferences nor run a public repository on github. Yet by many definitions of 'great', they fit the bill, but not the sort of 'great' that would mean companies would just 'know' of their greatness, and go out of their way to hire/recruit them.
And yet, I've known more than a handful of developers who are really solid, great people to work with, and I'd like to work with again. None of them have ever blogged, podcasting, presented at conferences nor run a public repository on github. Yet by many definitions of 'great', they fit the bill, but not the sort of 'great' that would mean companies would just 'know' of their greatness, and go out of their way to hire/recruit them.