But what would be the definition of "cloud" then? I'd say it boils down to managed services, so that you don't have to care about basic system configuration, hardware or networking. The only thing 37Signals outsourced is the hardware part and basic network infrastructure. That is pretty much what was known as "colocation" in the pre-cloud era.
But it was all just racks in a data centre before the invention of the cloud.
Yes, maybe the better wording would be "public cloud", still probably everyone reads this as "cloud" vs "private hosting"