CaptionKeeper may be part of the solution for webcasters. This product can take captions from television's line 21, and re-purpose them for the web.

In today's hot entertainment news, Disney has announced it will put their shows online, free. Any captions planned?

As far as I know, deaf/hoh people can not take advantage of the new download to own services, MovieLink.com and CinemaNow.com. I checked sample listings on both sites and there was no mention of the availability of either captions or subtitles.