Hardware is cheaper than developers and efficient code. But you're only as fast as your slowest bottleneck and all the current cloud solutions have fundamental performance or capacity limits we run into.
Could you do it well if building for the cloud from day one? Yeah sure, I think so. Could you consistency render all your pages performing several up to date queries and cache fetches across that cloud network you don't control and getting sub 50ms render times? Well that's another matter, and unless you're talking about substantially higher cost (at least 3-4x), the answer is no - it's still more economical for us to host our own servers.
And yes I realize that's a fun claim to make without detail. As soon as I get a free day (I think there's one scheduled in 2017 somewhere), I'll get with George to do another estimate of what AWS and Azure would cost and what bottlenecks they each have.
They say that hardware is cheaper than programmers. Wouldn't that speak for the cloud solution (software based scaling instead of admins)?