If DP's queues were empty and people eager to get more things to PP, I'd concur with you. As it is, I must disagree.
I have strongly criticized DP's queue management choices in the past. What I see now is: http://www.pgdp.net/c/stats/stats_central.php where my central concern, namely that the gap between books worked on and books completed was continuing to grow, representing a large and growing percentage of "volunteer effort being wasted" "stuck on queue" seems to be better addressed. IE looking at the graph back in 10/2008 something like 33% of the total volunteer effort was "stuck on queue", but now the percent volunteer effort "stuck on queue" is down to a more respectable 25%, and it seems like that is being managed to be about 8,000 books. They have seemed to understand the need to put more effort into postprocessing -- once you have made a large investment in getting a book to a near-done stage it is really important to push them out the door. I don't think DP has changed anything else so what I think they have done is simply reduced the rate of books accepted into the system in the first place, increasing the (implied) queue of books digitized but not begun proofreading. What this does, imho, is simply chase away volunteers who want to proof the lower rounds. But that is probably better than simply wasting those volunteer efforts by having too much stuck on queue in later rounds.