I'm hard of hearing, and closed caption support should either be added to totem or a dvd player that has closed caption support should become the default dvd player in ubuntu.
Right now, I've heard that vlc media player 0.9 will provide support for closed captioning. No other player that I can find supports CC or will support it in ubuntu.
Closed captioning is not the same as subtitles. Some dvds will have CC, but no subtitles for it.
Windows Media Center supports captioning, and so should the ubuntu media players.
Sincerely,
Susanna777
Edit: I have recently discovered the SMPlayer supports displaying captions, however it reads the captions data and displays it like subtitles. It makes DVDs with only CC accessible, however, I prefer the black box for better contrast and visibility.