There are many ways to make something successful. Simplifying for the masses is one way. It's not the only way.
For a conversion funnel, simplicity is better. The less a person needs to do to sign up or make a purchase, the more people will do it. It'd suck to repetitively fill out a form with your address, name, etc. every time you wanted to buy a song on iTunes.
On the other hand, if you're designing an application, the key is to have layers. Not layers like a conversion funnel, but layers of complexity. An app needs to be simple on the surface (i.e. Google), but have features available (but not prominently displayed) for people who want them. For example, Google searches the web. For a first-time visitor, that's all it does. For me, it's a calculator I use when I don't want to open up my application bar, it's a dictionary, it's a meteorologist, it's a way to search Hacker News, etc. There's a lot Google does with one input box, but it doesn't at any point in time force you to notice what it does. It just does it.
