I agree with many of Rod's points, although I don't agree that "The reality of the current economy is no doubt numero uno..." As Rod points out, these troubles have been brewing at the magazines for some time, long before the current economic downturn. I think he hit the nail on the head with the internet and the more connected amateur community of today versus twenty or more years ago.
One factor I didn't see mentioned is the growth of light pollution. People don't walk out of their homes and see the stars anymore, so they don't tend to wonder about them and actively go out to learn about them. As a result, the magazines are not gaining a lot of new subscribers.
As for my gripe with the magazines, S&T seems to have developed an annoying habbit of self promotion. A recent article on the discovery of Sirius B featured a photo of the aperture mask that former S&T editor Dennis DiCicco used to photograph it in 1970-something, which really added no value to the article IMHO. In another recent example, a reader question in the "Hobby Q&A" section asking why there are no green stars was answered with what amounted to "we answered that question in an article in our such-and-such month 1992 issue".