The main difference I see is that smartphones are built as playthings, stuffed with features that encourage addiction, but a real desktop operating system is built as a tool to help you work, and gives you all the access and power you need.

I see clear lines between things like smartphones and tablets, desktop operating systems, game consoles, and kindles. There's many different types of screens. I'm comfortable handing a non-networked laptop to my kid for her to play with, but wouldn't hand her a tablet or game console.