That is an option for folks for their future purposes. And some of them will indeed go with another company. This seemed a bit more underhanded.
Ok, maybe the package had things telling folks to always use HP ink and not a different sort. I personally would just pass most of that off as a marketing ploy. I mean, shampoo recommends I use their complementary conditioner after all.
Folks were indeed using non-hp ink with success - it isn't like the printer just refused to print with the replacements. If HP clearly stated that the machine wouldn't work with non-HP parts, it was obviously untrue.
Then a security update introduced the 'feature' that bricked the printers using non-HP ink. So one day, you find you simply can't print. Which is an annoyance if you are printing whimsical stuff, but not so great if you are printing off papers you need to take to work tomorrow or that you need for an immigration appointment or something like that. Suddenly, the printer doesn't work.
I think if it were an upfront, out-of-the-box thing (honesty and stuff) it wouldn't be such a big deal. It would be much like the DRM coffee pods. New machine, now with DRM! They didn't give the old machines an update, however, and take away the ability to use replacements.