Touchscreen for me is only the transparent layer over the LCD and that with a flat cable it connects to a hw driver that can be made from different producer (with of course different software driver).

So it is not so unrealistic the changing of these chips like they have changed IR chip, 3G modem chip, and so on.

Probably you when read something like "it uses original battery" think something like "there is the same nokia charging chip and so on"