Usability: Neccesary but not Sufficient
Commenter Albert D. Kallal makes a good point about Quicken being a useful product that broke new ground. Quicken did something useful: allowing regular people to do accounting without accounting arcana.
However, usability is not the same as effectiveness. A product that is easy to use but does nothing useful is not enough. Nor is usability (or effectiveness) alone enough to make a product successful. Other things must be there: the right price, support, marketing.
Usability types are prone to over-emphasizing the importance of usability: I am no exception. But good usability is hard to notice, and bad usability smacks you between the eyes, so it's not surprising that usability still has a ways to go. I stress usability because it still needs to be stressed: in an ideal world, it would always be an integral part of the process.