Presumably, because they were doing it line by line, and the Python version used C extensions (for performance reasons).

Yeah, we actually have a few cgo packages. We have OpenSSL bindings (we need to use our hardware accelerated crypto, go's crypto/tls lib doesn't support that (yet)), a faster CRC thing, we needed monotonic clocks and couldn't wait for Go 1.3, etc.

We'll be releasing a bunch of these. Particularly the OpenSSL bindings, which even without hardware acceleration are faster than Go's TLS library, and despite Heartbleed, OpenSSL is not vulnerable to timing attacks like crypto/tls is.