AFAIK the most important difference between WASM and other VMs on the level of CLR or JVM is that WASM has a simple linear memory model, which allows languages which expect a linear heap (like C, C++, Rust, ...) to be supported by just adding new backends to existing compilers (and most importantly without requiring changes to the language).

The CLR and JVM might be able to simulate a linear heap through a byte array (just like asm.js did), but it's questionable whether this allows the same performance as WASM when the whole VM instruction set is built around high level object references.