That option has been there for years - since the times when boot viruses were used, and there wasn't really any need to remove it. Besides, it's also scanning the modules loaded in memory (which might actually be why the switch is called "M", and what's the useful part of that switch).
I am not saying that you can't ask, sure you can... just that your effort/time devoted to find out isn't really worth the result you get, because the classical scanning of boot sectors is pointless these days.
Anyway, if you want to scan them from the command line together with other areas, then the easiest thing, as I already said in the other thread, is to specify multiple areas, including /m - without using the --task switch. If you want to include it in a task definition, you'd have to use the hack described above.