It won't be a... cloud?

To me, the principal differentiator is the elasticity. I start and retire instances according to my needs, and only pay for the resources I've actually consumed. This is only possible on a very large shared pool of resources, where spikes of use even out somehow.

If I host everything myself, the cloud-like deployment tools simplify my life, but I still pay the full price for my rented / colocated server. This makes sense when my load is reasonably even and predictable. This also makes sense when it's my home NAS or media server anyway.

(It is similar to using a bus vs owning a van.)