Linux also means higher hardware costs and bigger size and worse peripheral selection. Those are critical parameters in this market.
Yes.
> bigger size
If you're comparing something like a bare ATTiny to a Raspberry Pi, sure, but the size difference between a standard Arduino and the Pi isn't great.
> worse peripheral selection
Um, compared to what?
mbed, a new operating system, will have to have drivers written for everything it supports - which is likely much shorter list than for Linux.