I've had sites online since 1995 and I've used adsense since Dec 2003. Can't say I've made $10,000 to more than $30,000 a month as his site supposedly did, but if he was making that much money I hope he saved some. I have had non-internet businesses that did well for a number of years and then competition and other negative factors set in and they died. While they were going good, it was good money. I didn't complain when they went under. I had saved plenty of money and didn't carry any debt so it wasn't a big thing. As to the internet - It's changing. My sites are doing well, while some people's sites have crashed and burned. Sure, there are ups and downs, but year over year increasing visitors and increasing income.
This is no different than any other business except, in this case, the person depended upon AdSense and search engine rankings.
One thing I did notice is some in this thread mentioned his former site was "ad heavy". I can understand. There are some good sites out there that I just don't frequent because the ads have such a noise factor that it's just annoying. On my sites I set an ad limit. Right now if you'd go to my main site and visit the "Advertising Info" page you'd see a big "No Advertising is currently being accepted" statement which has been there for quite a while (about a year or more), yet I still get requests for ad space. I got another one last Friday. It's interesting how people react when you tell them I'm booked for the next year - They start into all the places I *could* place "...just one more..." ad. They even often offer to "double" my regular rate. To me it doesn't matter. I do not intend to diminish visitor experience by loading up a site with ads just because I can.
If could be that the gentleman killed his own site, possibly through greed, and now he is upset.
I stand by what I have said for years - If you have a good, quality site (or sites) with good content, and don't worry about SEO every day, if you make sure your visitors have a pleasant user experience, your site(s) will grow and hold their own against the competition.
Content and visitor experience, not SEO, is King.