From what I've seen, yes. It certainly didn't come from GW. I don't know what WH & WH40k look like now, but at the time that Magic was standardizing its language to avoid confusion (IIRC with the white-bordered "universal" cards vs the black-borded beta cards), GW rules were very vague, ill-defined, and prone to table arguments if you and your opponent didn't see eye to eye.Was this MTG innovation?
I never even realized what a helpful innovation it was (despite having played Space Marines/40k Epic for some time and gotten into many heated arguments with my best friend over how to interpret the cheesy eldar rules) until I saw it. We were playing MTG with the black-borderered cards with a stranger, and he adamantly refused to believe what we thought was a plain-english interpretation of one of the cards (I forget which, but we were correct ). A month or two later, the white-bordered set came out with rules that left no room for argument, and I had a lightbulb moment.