One of the three market tectonics I discuss in When Growth Stalls is the phenomenon I call changing industry dynamics. Nowhere are changing dynamics more evident these days than in the magazine industry.

According to Horizon Media and the Audit Bureau of Circulations, the number of paid subscriptions to digital versions of consumer magazines has nearly doubled in the past two years. That’s not a surprise, given the fact that the average U.S. adult has nearly doubled their time spent using the Internet since 2006 (from 2.1 to 3.8 hours per day).

Since there are still only 24 hours in a day, something has to give, and the print world has been hardest hit. The rapid decline in newspaper readership has been well documented, and even the most successful print magazines are cutting back. In a cost-cutting move, the New York Times Magazine recently trimmed its size by nearly ten percent, and Reader’s Digest (perennially among the top three in circulation of all magazines) cut its frequency from 12 times per year to 10 and will dramatically trim its rate base from 8 million to 5.5 million early next year.

It’s creative destruction in action. But not all magazines are sitting still. Horizon also reports that Men’s Health is introducing an iPhone app that will distribute paid content, a first for the industry. If it’s successful, no doubt others will follow. Even good ol’ Reader’s Digest is getting on board, planning to plow some of its savings into mobile apps and topical digital editions.

Rapid change can be both fascinating and disconcerting at the same time, like suddenly being able to see the secondhand moving on your watch. But these media companies are simply responding to a changing world, and it’s changing because we’re changing.

As always, what works will stick, and what doesn’t, won’t. As it should be.