"No selling his soul to a publisher, no middlemen, just pure income, controlled directly by him."
Actually, I'd like to point out that the income is NOT controlled directly by him. It's controlled by the company doing the advertising, and can be taken away by them at any time for any kind of TOS violation. This income stream is a side effect of the popularity of this particular game and the (relatively recent) ability to make money selling advertising.
I'm just saying that there IS a middleman. Have you seen Google's profit margins lately? So maybe the split is a bit closer to 50/50 than 15/85 like the railroad tycoon author (which is also very close to a recording artist royalty rate, btw), but it's not a physical product either, with the additional overhead of printing, shipping and selling shrinkwrap at retail.
When that popularity goes away (as it almost surely will eventually) so does the revenue, and having one hit is no guarantee of having a second hit. Fortunately, he (the programmer) is aware of this, and he mentions in the interview that he'd probably have to make one new game a month to continue to make a full time living at it. But how many original (or even unoriginal but executed well) concepts can you come up with before burning out? 10? 20? I think the lack of graphical sophistication works for this particular game but will undoubtedly be a disadvantage for any others he might make.
Anyway, I don't see it as a business opportunity at all, really. Building it and hoping they will come is not a business model that I want to rely on. Nobody is going to quit their day job to make money doing this unless they can already afford to not work for a few years. It's a way to make some money from a hobby. Only after you get a hit, THEN just maybe you can have the confidence and financial cushion to get more serious about it. That's just my opinion though.
I also have a serious issue with the fact that the only business model available to individual developers involves doing something that attracts enough attention to sell advertising. Maybe I don't want to make a living facilitating that! Is there any way to achieve independent success WITHOUT resorting to advertising? That is a more interesting topic to me.