I guess that has a very good reason, "modern" devices are simply to flat to have any mounting points.
I find this an odd development: We're trying very hard to make our UIs more and more 3D, up to the point of sacrificing usability. And at the same time we're trying also very hard to make the devices using these UIs more and more 2D, also up to the point of sacrificing usability. I'd imagine it would save us a lot of trouble if we stopped both of these attempts.

I guess that might be true if you use absolute pointer positioning, like you typically would on a touch screen. However, if you use relative pointer positioning like on a laptop's trackpad I don't see why the inaccuracy of a capacitive screen should be a problem.
Think of the N900's/Jolla's touch screen as a transparent trackpad, that just happens to have the screen underneath it!
It would even give potential for increasing the pointer accuracy (at the slight expense of speed and intuitivity), regardless of the screen technology.

Where can I get certified for judging what's essential for others and what's not?
Might come in handy sometimes, though not necessarily when talking about smartphone features.

Capacitive screens tend(ed?) to have a lower "input resolution" than resistive screens.
Theoretically with the stylus I can control my N900 at pixel accuracy. Practically I get something between 3 and 5 pixels due to my shaky hand and not enough diligence during calibration.