At the NABShow last week, I interviewed RAMP's CEO Tom Wilde about why closed captioning is coming to online video as a result of the Twenty-First Century Communications and Video Accessibility Act from 2010. The Act specifies that any video broadcast on-air after April 30th must have closed captioning by September 30th if it's placed on the web.
Tom explains that given broadcasters' existing analog and digital work flows, creating closed captions for the web creates huge challenges, which RAMP's Media Cloud addresses. The good news is that research shows that closed captions give viewers more control and therefore are also more engaged, driving a higher ROI.
See video below (5 minutes, 19 seconds)