I have a simpler theory, one that was presented by Bruce Tate in the Ruby on Rails Podcast back in March of this year. He said:
You can either look at a programming language as a means or as an end. And if you're looking at a programming language as a means it's just a tool to get a job done and religion just falls out of it. But once a language is entrenched and that language becomes a meal-ticket then the language becomes the end. And when that happens you're gonna get passions stirred up whether you want to or not, because now when you threaten a language you're threatening somebody's ability to feed their family...
I wouldn't present it quite so dramatically as being unable to feed one's family, afterall Java isn't about to be replaced any time soon, but I think his position is probably correct. Java is a meal-ticket for a lot of people. Many have worked their way up to nice lofty "architect" or "senior lead" positions. Most of them through hard work. They know Java and the frameworks and tools that go with it (JSF, Hibernate, Struts, Spring, Eclipse, IntelliJ, Tomcat, JBoss, JUnit, etc). They've made a significant investment and may quite naturally feel threatened by something like Rails whether they realize it or not. It challenges their position and knowledge.
Andy Hunt, one of the authors of "The Pragmatic Programmer" said:
Languages and frameworks come and go, but your habits--your practices--stay with you for your whole career.
Unfortunately, most people don't understand that. They look only at what's directly in front of them and don't check the horizon to see what's coming. Today Java can be a morass of complexity and it's only by looking at things like Rails do we challenge our preconceptions and make our day-to-day Java development positions better.
Keep giving the presentations, continue to push the boundaries. People don't like to be pushed but constant gentle persuasion will eventually leave its mark.