It is difficult to hold candidates to their words, when their words are already gone on the wind. Discourse is reduced to dueling sound bites. Web pages are persistent. It isn't enough for them to look good, or sound good. They have to stand up to scrutiny and criticism.
Active TV is a passive medium.
Viewers sit in front of the screen while sounds and images wash over them. The broadcaster decides what they see and when they see it. TV purports to provide information, but what viewers mostly get from TV is emotional impressions. Users decide what they see and when they see it. The web invites reflection and analysis.