This is correct only if you run "Hello World" apps on a single server. PHP scales horizontally so any real-world application can easily scale to 10, 100 or 1000

This is correct only if you run "Hello World" apps on a single server. PHP scales horizontally so any real-world application can easily scale to 10, 100 or 1000 servers. If there is no other scaling challenges (like databases) then it can scale forever thanks to its beneficial process model.