Direct mail: declining effectiveness?

The Economist reports that studies indicate a drop in direct mail effectiveness:

The response rate from some campaigns has fallen to just 1.4%, according to America's Direct Marketing Association (DMA). In previous years it was well above 2%. When it comes to responding to “direct-order” mail shots (signing up to an offer, as opposed to merely expressing an interest), the rate has fallen even more dramatically, to 0.7% from 3.5% in 2004.

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The report says (quoting AdAge) that the drop may be due to mailbox clutter, "leading many consumers to discard the blizzard of solicitations they receive." While I can certainly testify to having a cluttered mailbox, I wonder if the clutter is that much worse than the recent past.