Well, think again. It happens all, aaalllll, the time. But Unity’s marketplace is so large that people quit jobs when selling plugins that are well received there. Thus fixes are pushed very fast;
However I ensure you none of a dozen plugins I’ve done for Unity 4.5.x are working 100% on 4.6 and also barely work on Unity 5 if at all. I can’t keep investing time on them anymore so I’ve made them free for 4.5.x users. If they want a fix they do itself because source is all there.
And, well, I can only speak for myself; I won’t ever buy anyone’s for UE4 if it is closed source.
I already regreat I paid for RadiantUI 