To most people "reaching scale" means either revenue number or number of customers (word "when" implies that).
You can easily reach "scale" (earn millions of dollars, serve millions of customers) while still running on 2-4 web servers.
You can easily reach "scale" (earn millions of dollars, serve millions of customers) while still running on 2-4 web servers.
But I've done it with Python and I can't see why Ruby would be any different.
Why is that so surprising? Nobody sane does anything CPU-intensive in their webapps.