This is an interesting thread.
As far as ADVRider the site goes, it's really not just an ADV focused site. It's probably one of the most comprehensive motorcycle and general discussion sites on the web these days. I visit it nearly every day just to poke around. There's a lot of cool discussions there on all kinds of topics.
As far as a decline in ST bikes and a rise in ADV bikes, it would seem so. I had a Concours 1000 for six years, and put a ton of miles on it, riding all over North America, and I got bit by the ADV bug in 2009. I bought a Buell Ulysses. I had wanted one for a long time. I thought they looked cool, were kind of unique and unusual, and I thought I wanted that style of bike. I had it for five years and disliked it more each year. Some of that was the Buell - I had a lot of problems with it. But eventually I came to realize that the style of bike just wasn't for me. It was really fun to ride, handled great, lots of torque, but I hated riding it long distances. The wind protection wasn't good, even with farkles, and it just tired me out to ride it a long way. It was really cold in early and late season riding, even with heated gear, and I have short legs, so that kind of bike is difficult for me. I ended up getting rid of it this year and buying a 2003 ST1300. I keep asking myself why I didn't buy an ST five years ago. I absolutely love it. It's the perfect bike for me. Sure, I'm not going to do much if any gravel on it, but I rarely took the Buell on gravel either for that matter.
The large ADV bikes are cool and aggressive looking, but to me, they just aren't as good an overall package for the type of riding I do, but a lot of people like them, so what do I know? The funny thing is, the guy I bought my ST from had purchased a brand new BMW GS1200, and his wife was not happy he was selling the ST - she doesn't like to ride on the GS.