I believe that link juice is meant as an expression of how much of a Page's PR is transferred by a link.
This will vary according to the number of OBL on the page etc.
Bing (yahoo) has its own system because it has a different links database to Google. I have seen references from a couple of years ago to "Page Score" but can't find it displayed anywhere now. But they will have their own metric, even if it isn't available in toolbars.