Maybe I'm naive and I surely don't know anything about the WASM spec, but aren't CPUs implementing both exceptions and tail call elimination as gotos (some jump machine code instruction) ? Exceptions might have to pop some frame, TCE doesn't.
To avoid some classes of security issue, and also because it started much closer to asm.js in features, WASM uses structured programming control flow like blocks, if..then, and break statements. Functions can only be called by the call instruction right now, so this proposal is needed to jump to an function body.
