Well, I just like the idea of being relevant to the person visiting the website. Building a hub of information. Sure, I would promote products, and these money pages would do well but I love the idea of building a nice internal linking structure with some nice support pages explaining how to use the product, and how to solve some of the issues you could face with it. So while I personally think you could rank a one page website, I do think a multi page website is more feasible in the long run if you tend to start a real business. I intend to become an authority figure in the niches where I start, and even though I completely agree with the fact that you can rank a one page website, I do think it is far more scalable to rank a multi page website as you can also target way more keywords, and increase the organic traffic to your site. but that is just my 2 cents. I've heard plenty of people having success with one page websites, its just not something I would go for.