It's much more than just that though. If you scanned Express feature by feature you could implement most of them in Go. I would imagine someone experienced in JS and Go could port the entire thing over in a day.
It's just then what? Now you have:
1. Similar / worse performance.
2. Way less useful libs to leverage.
3. Have to write 2 languages instead of 1 (if you happen to already use Node).
4. Dealing with way less mature libs for crucial components that you definitely don't want to be writing yourself.
There's basically no gains. Deploying single binaries is great but a "write once, use nearly forever" build script makes deployment a snap with any non-compiled language.
Testing support is amazing in JS too and debugging is leap years ahead of Go. Using gdb is just archaic compared to using node-inspector. I'm sure Ruby and Python have equally as amazing testing/debugging support too.