Although, I will say that Vala plus GTK+ is amazing for desktop development on Linux, especially with elementary OS's Granite library. The thing is, it's really just a nice language on top of C plus GObject as a transpiler!
I do wish that some other languages were as nice to use as various scripting languages, but with the performance and pure utility of C/C++. Maybe one day.
Oracle's Project Graal plans to replace the C++ JIT by a Java one. This is based on the work of the Maxime VM.
Much more info about the compatibility and differences for anyone interested on wikipedia[1].
[1] http://en.wikipedia.org/wiki/Compatibility_of_C_and_C%2B%2B
I just think that their names, common syntax and saying things like 'C++ is a [sort of] superset of C' make people unfamiliar with them think that they are more related than they are. That's why I brought up Python and Ruby - two languages that are different in syntax and many details but in the same conceptual space, whereas C and C++ look more similar, sound like almost the same thing but are, conceptually, on different planets.
The developers of MRI are focused on developing an interesting and useful language first and everything else second. The developers of JRuby are focused on replicating that language on the JVM. They benefit from a sophisticated JIT and GC and in later JVMs some direct help, none of which diminishes their own efforts to improve performance.
Sure you can write slow code in anything but I don't see how that's in any way related to 'your JRuby/CRuby' comparison.
By that logic, any mention of any difference between any language, runtime or its implementation can simply be dismissed by 'well, they ARE all Turing equivalent!'
I just wanted to point out on your previous comment - it is not surprise that only choosing some particular language doesn't mean a guaranteed performance.