Yes, legacy systems are usually that because they work. Last year I worked with a COBOL organization just now looking to upgrade some of their operations.

But you are right, RoR doesn't have the full depth and breadthof the API's, etc that Java does. But the question is... does it need them?

Bruce Tate lays out the scenario that on the lower end CRUD-database type stuff is one of the areas where Java is especially threatened due to its sheer complexity to get rolling. Rails, PHP, or Python on the other hand...