One of the important features about Google Reader is that it's generally one-way; yes, I could comment on the original items for many of them, but I have way less desire to than LW posts.

A related massive productivity gain from Google Reader is that it is very easy to make it only interfere with your day once at a scheduled time, and you can just forget about the sites for the rest of the time. There's no routinely checking to see if something new has shown up, with the associated variable reinforcement, but that means it's not as appropriate for media where two-way communication is frequent and opportunities are transient.