Ultimately, this list will include Hulu, ABC, NBC, Comedy Central, Fox, et al. We will have to wait for the content providers to decide that advertising to web viewers is just as worthwhile as advertising to cable viewers.
No it won't, None of the large networks are moving to this model anytime soon. This is not a matter of loss of ad dollars its a matter of loss of subscription revenue. Cable Networks pay the networks to carry their content (ESPN make $4B a year in cable fees) and ad dollars on the web in no way make up for this loss in revenue. You may end up getting everything on demand some day, but you will be paying a subscription for it.