FWIW I trust that the numbers were good when the Google and Mozilla folks gathered them, but I had nothing to do with numbers!
In particular, I haven't looked into validation. JSC doesn't treat asm.js any differently than JavaScript, so the comparison would be different as well.
I note that the comment in 7.3 says the biggest speedup vs asm.js is in validation, so I assume this means the measurement includes startup. This advantage is easy to concede to WebAssembly due to its design.