Of these, only GitHub, Mailchimp and Auttomatic have less than 1000 employees. All have more than 500.
(That doesn't mean that Twitter isn't too big or grew too early, but it does mean that none of those nowadays qualify as "see how you can run a big product with 30 people")
You're making a stretch, here. The difference between 100 to 500 or 1000 is exponentially different than the difference of 100 to 3,700. They don't need this many people. Period. This is a "who's dick is bigger" contest over a thinly veiled (and absurd) justification of infrastructure. No one outside of this bubble buys this shit. There are global supply-chain networks that move millions of products, and they don't employ as much as a micro-blogging platform. Come on, now.
(That doesn't mean that Twitter isn't too big or grew too early, but it does mean that none of those nowadays qualify as "see how you can run a big product with 30 people")