The major new features, as I perceive them, coming in Java 8 are Lambdas and the Stream API.
Given that I can leverage such features on the JVM using Scala or Groovy etc. etc. is there anything that might compel me to continue to use Java over these other languages?
I don't think that happy Scala and Groovy users will say "oh my, now that Java 8 has lambdas, I will return to my childhood love" :-) There are other reasons why you use Scala and Groovy, and those haven't changed.
But most people have not made the switch away from Java, and for good reasons. Java is good enough for many purposes, has a huge base of library, great tooling, and lots and lots people know how to use it. It's not going away any time soon, and if you work with Java, you'll love Java 8.