As a side note I've seen it happen here on this forum. Members will use 95 percent of someone else's recipe and methods, tweak something and claim to make it better, and not give any credit where it's due. Then new members start trying that person's recipe and everyone forgets who started it originally.
I've seen it with topping combinations, whole recipes, parts of pizza making methods, oven mods, you name it. Myself, if I have been inspired I will usually mention the source of the inspiration.
As far as restaurants doing it, I don't think its wrong. Maybe unethical, but fairly common and expected nowadays.