Some people, and/or companies forget to update it, or don't.
For example Powerbullet Presenter it worked perfectly on my vista home premium and ultimate, but they still haven't updated the OS requirements, which are, Windows 98/ME/NT/2000/XP
Legally they have to but... If it doesnt have it then its not meant to run on that OS so... (even if it happens to seem to run on it)
I even notice you run stuff and/or test it just to see which is a bad thing and you shouldn't do that at all but..(unless you have ok test systems to do it on..not your main ones) Eventually it will end up screwing something up for you and on you and in a very bad way if you keep doing that. You will end up coming across one that just totally crews your system.