But "open" does imply having more than just one realistic choice, or at least the ability to realistically create more choice if it isn't already present.
Right now, JavaScript is basically the only option in practice, and getting additional languages supported by the major browsers does not seem possible. I don't consider that "open" at all.
That's completely ridiculous, nothing about the word "open" implies that there being multiple VMs.
> Right now, JavaScript is basically the only option in practice,
That's absurd, Opal is a real option. ClojureScript is a real option. There are real, functional apps written in them. Prismatic, for example. There's far more language choice on the web than any mobile OS.
JavaScript is not a real virtual machine by any means, even with efforts like Asm.js and Emscripten being considered, and even if the recent implementations have been drawing ideas from real virtual machines. Compared to real virtual machines like the Java VM or the .NET CLR, it's very, very lacking.
At best, it's merely an interpreter that's targeted like it were a VM, since there is no other practical choice within web browsers today. This is part of the near-total lack of openness I referred to, by the way.
And it's very absurd for you to suggest that "there's far more language choice on the web than any mobile OS". That's not true at all, given that every major mobile OS today includes a web browser of some sort that can run web apps. And then the mobile OSes still allow the use of languages like Java, C, C++, and Objective-C, among others. So the choice is clearly far greater on mobile OSes, given that they support so many languages, plus JavaScript.
Right now, JavaScript is basically the only option in practice, and getting additional languages supported by the major browsers does not seem possible. I don't consider that "open" at all.