Multi tasking, multi threading and multi processing... I think on background task multi tasking Windows Mobile does a steller job. Push notifications for instance are at least 5 9's reliable. Updates. Not sure if background tasks count though or is this referring to UI experiences/multiwindowing? Sorry I have not read the whole three yet. But what you said is true. iOS is a killer at this and why battery life is excellent on their hw.
Yeah, I wasn't referring to services, like notifications. But rather "apps running at the same time, in real-time". Mobile OSes generally avoid this because its a battery hog. Android has a system where it keeps some apps in ram, still running, but sort of "decides for itself" whether to keep them there, or freeze them. However it also discourages developers from using this.
iOS and windows 10 mobile, generally just freeze, with a few specific exceptions like music playing and navigation. BB10 runs up to eight apps real-time, its the closest to the desktop experience of multi-tasking. If you run a bb app, it keeps going no matter what it is.
For most people, it wouldn't much matter generally getting real-time. The average person might want to keep their music going (works on all platforms), or perhaps stream something (works on some not on others).
But the sort of power user "crunch video here, install software here, run a youtube video, whilst skyping" doesn't generally find much use on something with a tiny screen. And they both offer benefits and advantages. iOS generally has excellent battery life, and I suspect win10m would be the same. They'd also both use less ram. But the odd user might want multiple things running real-time, for which windows 10 proper and OSX are the best, and bb10 and android have a limited capacity.
It, like most things mobile, are a series of compromises. For which compromises one wants, like the cheese block sized phablet, versus the pocket 5 incher, it depends on the user which they will find the best.
Myself, I basically very rarely want anything real-time on a phone. Very few apps are designed to run that way anyway. Battery life is my priority there, so on a phone, I prefer a system that freezes apps. On a tablet, its a different story, and PC different again.
The ideal smartphone system, at least until the battery life gets to a week or so (long way off lol!), would be one that actually lets the user decide between bb10s, androids, and windows10m/ios's system. A toggle that lets you choose how many apps to keep in real-time if any, and whether to throttle services and to what degree. Something like the UAC settings in windows (a slider), but with battery optimisation.
Although for me, I'd always turn it down to the bottom.
But if they decide to scale windows proper, via arm, onto eventually a smartphone platform, they really should do something like this. And have a setting for plugged in, versus not plugged in. This way one could have the full desktop experience, or a more battery optimised system, depending on what one wants, and whether its docked.