Sure, but UI needs to reflect that too. I just opened Steam to verify - it definitely says 'Buy {game_name} - Add to Cart'

I remember saying the exact same thing here on HN like two weeks ago, which someone then promptly corrected me saying that Steam/Valve actually "explain" what their "Buy" means right before payment, and I think they were right, there is some greyed out text somewhere explaining you don't actually "Purchase a copy of the game" but you license it via Valve/Steam somehow, can't remember the details atm, later at the checkout process though.