Thanks for pointing that out. I hadn't realized Microsoft had jumped on the Docker bandwagon to that extent; it's far enough from the topic at hand and from anything I'd ever use that I overlooked it.

So while there is in fact an exception to my previous generalization, there's still no cross-platform compatibility magic to Docker aside from that of virtual machines. If the container OS is different from the host OS (or a different version of the OS, for Windows containers), then using Docker is an instance of using VMs, not an alternative to VMs.