You're right, but there is a lot of misunderstanding around this end of the market, mainly because advances have blurred the traditional segmentation. When talking about ARM, the 'M' in Cortex-M means 'microcontroller' whereas the 'A' in Cortex-A means 'application'. Cortex-A systems are often at the centre of 'System-on-Chips' and will run linux, and indeed the NT kernel as well, as they are bundled with enough RAM and fairly modern peripheral interfaces such as HDMI.

Cortex-Ms typically can't run linux (excepting uClinux) as they don't have the RAM and typically don't need to as they address a different need (dedicated function instead of general-purpose compute), and have far fewer peripheral interfaces. It used to be all about power profile, but the recent SoCs are getting pretty competitive there as well.

But as I said the traditional segmentation at this end of the spectrum is being re-cast seemingly every second week, and so terms such as 'microcontroller' are becoming less meaningful all the time. And who the hell can agree on just what 'embedded' means these days?