I agree, Luke, this is exactly what I think has happened. The sales figures themselves are from CIPA, so I presume they are correct. It's pretty simple, methinks. We've reached a point of diminishing returns with camera improvements and 16mp really is a kind of sweet spot. So those who are pretty serious about photography - whether pro or hobbyist - have less reason to upgrade.
For the masses, smart phones - which themselves have reached a sweet spot in terms of price, availability and picture-taking ability - offer the convenience that really is the most important thing for them. These people were Instamatic and Poloroid camera buyers in the 1960s and 1970s.
Add to this the economic situation. True, the U.S. is technically in a growth cycle, even if a weak one. But I can only use myself as an example. I weathered the financial crisis and recession fairly well. But it is in this year - 2013 - that I find my flat salary and rising expenses have caught up with me. I have far less money to blow now than I have had in quite a while. so camera purchases go on the back burner, especially since I have a nice kit already.
Perhaps now we'll go back to something closer to the more-sane world of photography prior to the digital age. But, with a camera market that's shrinking as fast and as much as it is, some players are likely to fold.