Actually, all of those have something strongly resembling a kernel, and DOS in particular makes a nice distinction between the basic services (BIOS) and whatever userland you choose to install on top of it. I think you're making my point - "Operating System" used to mean the "kernel" before RMS wanted to ride on Linux's coat tails and Microsoft wanted to bundle their browser anti-competitively - both of which are distasteful.

Depends... if the conversation is a short coming in any part of Linux that isn't the kernel, then Linux means the kernel. If it's something positive, then Linux is the kernel, boot code, userland, and anything else that can be fit under the umbrella.