Sun was all about Java and I think it's disingenuous to say that Sun ever threw any significant effort into JRuby further than seeing JRuby as a way to assimilate Ruby into the Java Borg.
I have no idea what Sun's motivations were (and I doubt you do, either), but all the time I've been using JRuby I never got the sense there was anything going on that was designed to hook people into Java other than using the JVM.
There was no more assimilation going on than what I would expect to see from Apple and MacRuby. Less, perhaps, since JRuby apps run on multiple platforms, something MacRuby apps won't do.
And since JRuby itself was nothing more than a jar, developers could slip it into their usual Java environment without having to explain how or why they were installing Ruby.
I've sat in JUG meetings watching JRuby explained to Java fans, and each time they crowd goes from notable skepticism to smiles and head-nodding when they see what they can do.
Sun's support of Charlie, Tom, et al really helped get JRuby up to speed making it not only the fastest complete Ruby implementation but also acceptable to "the enterprise".
Sun may have been all about Java, but to the extent they helped JRuby they've enabled many Java devs to be all about Ruby.
