Hey don't forget Groovy. If you have ever liked Ruby but don't want the weight of JRuby, try out Groovy. It made big waves before Scala.
Before Groovy was Beanshell, which was Groovy's inspiration. And of course Groovy's creator, James Strachan, did say if he'd known about Scala at the time, he'd never have created Groovy. And Groovy's quite weighty itself, have you seen its Antlr grammar file?
So? He's talking embedding a small scripting language into a JVM project. Groovy fits the bill, Scala doesn't.
FWIW, a quick run of the binarytree benchmark shows luaj as slightly faster than luajit on my system, but does it matter? Not many projects have a realistic choice between lua/luajit and luaj, unless the whole thing is written in Lua.