Thanks - appreciated.
I think part of my confusion is that someone (mentioning no names to protect the guilty) has removed the documentation for js_init_call() from the docs and replaced it with the yui_module documentation (this page http://docs.moodle.org/dev/JavaScript_guidelines, got to go back a bit to get the 'old' docs http://docs.moodle.org/dev/index.php?title=JavaScript_guidelines&oldid=38075)
It's hard to tell if this was intentional or otherwise. As you say, the third is new and unused. I'm not even sure I fully understand what a 'YUI Module' actually is.
Anyway, as a more general point we should be wary of removing documentation for features that are heavility used even if they are no longer the "flavour of the month".
This leaves me wondering (it doesn't say) if js_init_call() is about to be deprecated in favour of yui_module()? Dunno!