That's true enough, but in closed-source land it's a given, basically (unless you fancy reverse engineering or writing from scratch).

At least on Linux there's a *reasonable expectation* that if there are developers willing to keep a device alive, it'll happen - if the manufacturers will meet them half way, at any rate.

edit - also worth pointing out that Windows support cycles (meaning both security updates and availability of modern software) are generally longer, although Linux support cycles do seem to be lengthening too.