I think it is the sitting....the article talks more about the long period of inactivity more than the television.
We sometimes ride an exercise bike while watching television, and I think if you kind of broke up the evening (say rest on the butt for an hour after dinner, than get on the bike for an hour, then rest for an hour and then finish off with 30 minutes of bikiing before bed) would probably nullify the negative health effects.
It appears 4 hours of complete inactivity is the really bad point, while 2 is much less serious.
More info on this subject...
http://www.consumerfreedom.com/news_detail.cfm/h/4073-the-latest-roundup-on-roundness