It's sort of misleading in a way. You certainly wont be able to develop the same pressure without one, but that technically doesn't matter unless you find yourself suddenly having to squat your max weights without a belt... and I'm not seeing how that happens.
Activating more of your core (with a belt) should mean that your core actually gets stronger... but yeah, you still wont be able lift as much without a belt.
There's nothing wrong with the suggestion that they're only used on your heaviest sets though (this counteracts the problem of not getting used to bracing without one, because obviously on your lighter sets you'll still need to get your form right).
Edit - Hell, reference could even be made to the fact that the subject is under debate.