It's not certain that Valve will always double-check game submissions to make sure they honor the policy when it takes effect in the next few weeks. However, this at least gives the company the power to force changes (or in the worst cases, pull apps) if it sees a game that violates the new rule. If nothing else, Valve is practicing what it preaches. The Dota 2 product page on Steam now focuses on in-game screenshots where it previously centered on illustrations.

This doesn't guarantee that every sketchy developer will mend its ways, or that Valve will avoid selling games whose massive hype doesn't quite match reality. It should discourage studios from trying to hide shoddy graphics from customers, though. That, in turn, should reduce the chances that you need to ask for a refund or otherwise suffer through buyer's remorse.