I suppose it depends on whether you're thinking of an adversarial situation, or assuming sites that don't actively try to defeat the user's preferences.

Most news sites don't try to defeat my adblocker, to offer one example. It would certainly be in their interests to do so, but it's rare that they actively try. When they do, they usually try to block access while asking me to turn it off, rather than trying to sneak ads past it.

I'd probably stop visiting a site that actively tried to force video to play when I've asked my browser not to.