In case you're curious, though, there are a few reasons I think lower advances have been—and continue to be—the norm.
Belt-tightening. With forbidding economic indicators such as unemployment still high and talk of a double-dip recession floating around, editors and publishers have become much more frugal in terms of the advances they offer. Many have modified their P&Ls to reflect current sell-through and consumer habits, and decreased demand for physical books has resulted in decreased up-front cash for authors.
Publishing is a business, and we've got to try to make money on as many books as possible in order to stay in business. Speaking of physical media, another reason (à mon avis) for lower advances is:
The shift to electronic media. Because e-books don't face the same kind of supply chain/distribution challenges as physical books and are not returnable, it's easier for publishers to run P&Ls for e-books and to simply offer higher royalties than to stick with the advance model.
True, the vast majority of titles currently acquired are eventually released as concurrent physical and electronic books, but I don't think the day is long off in which a substantial section of the market will comprise e-only titles. Once that occurs, I think the idea of the advance will become even more antiquated; it's much easier to pay an author a fixed percentage of dollars earned in the more or less real-time environment of e-book sales than to bother with advances.
In fact, much (though certainly not all) of the work done by advances is obviated by the fact that:
Advertising and marketing budgets for e-books are often lower than for physical books. While a publishing house—particularly a large one—will pay the advertising and marketing costs for their lead titles, there are many midlist titles and titles published by smaller publishers for which the burden of lining up media and marketing falls squarely on the author. The advance is a way of mitigating this hardship; authors can use the money given to them by publishers to pay to promote their books (e.g. conduct book tours, create book trailers, and so on).
As advertising and marketing have become easier and cheaper—predominantly by way of social networking services like Facebook and Twitter—the cost of promoting books through these channels has necessarily also fallen. If publishers feel they can pay less money for the same commercial success from any given title, they absolutely will. Wouldn't you?
So that, dear readers, is my take on why average advances seem to be declining in this industry. It may be a relatively short-term reaction to the continuing economic uncertainty inherent in the recession, or (as I believe) a long-term reaction to the drastic changes that are occuring in the publishing industry as it transitions from physical to electronic media. Regardless of which, I think it signals an industry-wide recognition of the challenges the business is facing.
What do you think, gentle readers?