ABC's decision to hold back inventory follows NBC's admission that it would so in May, though, not surprisingly, neither network has said how much more of the traditional 20 to 25 percent held back for scatter was in the offing. But they probably aren't the only ones. I don't think BNET Media's corporate overlord, CBS, has said it's holding back inventory in so many words, but CEO Les Moonves basically hinted at this strategy at a conference back in March; I can't imagine that Fox isn't following suit.
Another reason to hold back inventory for scatter is to get better prices now by cutting supply. While single-digit CPM decreases is what the networks have had to agree to, they haven't had to take the double-digit drops that advertisers wanted them to several months ago. There are many reasons for that -- one being that neither side ever completely wins -- but holding back inventory may well be another one of them.