CD all that matters

It seems as though mana cost is really an irrelevant thing nowadays. So many champs don't even USE mana, and the newer ones that do can spam away even at early levels. (XelKoz OMFG!) What is the point of making a mage miss when they can just keep spamming away and hit with SOMETHING eventually? Earlier seasons players had to learn to budget their mana a bit. Why did that go away?