having to run multiple instances of a web service for ruby/python seems like a hack to me
Since we are now moving towards more cores, rather than faster processors - in order to scale more and more, you will need to be running more instances. 
So yes, I reckon you are wrong. 
This does not by any means condone brain-dead programming with the excuse that you can just scale it horizontally, that just seems retarded.
Is it just me or is having to run multiple instances of a web server to scale a hack?
Am I wrong in this?
Clarification
I am referring to how I read people run multiple instances of a web service on a single server.  I am not talking about a cluster of servers.