I have no first hand experience, but I'd guess the widespread use of SMS text messaging was a much bigger boon for those with hearing difficulties. Not quite as "sexy", and difficult to portray in an ad (particularly as you'd be even more insane to try and claim this was an innovative feature of your platform) but still out there making people's lives better. I'm fairly certain the same is true of the web generally despite occasional steps backwards with Flash, unsubtitled and untranscribed audio and video etc.