Harass your users... and they'll go elsewhere.
HP made its best to push its customers to competition - the "time bomb" that triggered the refusal of tird party inks is an excellent example.
Moreover HP got out from the high-end inkjet printers (pro photo printers), leaving that market to Canon and Epson, which are delivering excellent products (with their expensive inks). Users of this kind of printers may be less inclined to use non original inks, and risk less reliable output and prints longevity.
Thanks for the hint about looking for the usual hidden commands...