"Laws, like sausages, cease to inspire respect in proportion as we know how they are made." [0]

There have been many variations on this quote; the one I like best is "Those who love sausage and democracy should not see either being made."

[0] http://en.wikiquote.org/wiki/John_Godfrey_Saxe

I'm assuming Bill left out specific numbers because he doesn't want to share them. "Watching the sausage get made" just means he got to see all the details that went into building Twitch.