This is nice in principle, but look at the limited data available:
1) Bookstores may discount books that get old and don't sell, but aside from publishing lower quality versions (e.g., paperback), there's no real history of the publisher lowering the price -- jacket price on a hardcover bestseller from 2000 is not substantially lower than the jacket price on a 2010 h/c bestseller, is it? And it's the publishers who are controlling the price in this agency model, whereas the store owner equivalent -- like Amazon -- now don't control the price.
2) The closest digital analogy to this situation is variable pricing in music, and the dearth of $0.89 songs in the iTunes store seems to argue against anyone's intent to discount pricing to maintain sales.
If it happens, then fine, I'm okay with it. I just don't trust the publishers to do this at all. Meanwhile, when I bought new hardcovers, they had an average price around $10... I didn't pay $15 for hardcovers. I'm fine with variable pricing, but in the case of the iTunes store, variable pricing just meant the average price went up, whether you buy old songs or new ones. I'm not okay with that. If the publishers will really discount progressively, I'll believe it when I see it.