A WSJ (subscription only) column explains the issue WRT to telephones, but the point applies to all media that transmit information at the pace of speech:
. . . Given a choice, who uses the phone anymore? Talking — whether on a cellphone, a landline, or some VOIP-y instant-messenger doodad — can be time-consuming and ponderous, and costs money. E-mail is a cold and barren medium, but it’s efficient, and we don’t have to wait for the bozo on the other end to hang up — we just hit escape. Anyway, we can read much faster than we can listen — all that spam in your inbox is annoying, but just imagine if it were voicemail.
Not only can we read much faster than we can listen, but with text we can easily read ahead or reread what we’ve already read. Simple and efficient.
Text is for communication, speech is social. While speech is useful for communication, text tends to displace it in uses where efficient communication is more important than sociability. For example, text messaging and text email access are popular cellphone features but email-to-voice translation never took off.
The use of text to transmit information will continue to increase as productivity increases continue to make everyone’s time worth more. The model for the future is not video blogging or video phones but specialist blogs and RSS feeds, and other text-based information filters on the margins of the network. Voice and video will remain the province of calls to your mom, business meetings, some news reports and a narrow range of other applications, where the social information conveyed by speech or the visual information conveyed by video is valuable enough to outweigh the speed advantage of pure text.