Here are two simple economic arguments for why all the innovation in hot new web technologies comes from user/consumer oriented web applications.

1. At the low end of the market, prices and market size often will not carry traditional advertising or other kinds of marketing to increase your user base. You can only market virally. Viral=>Attention=>Experience focus.

2. Getting paid at all for web services in retail is often difficult, so you need to rely on advertising income. Advertising=>Attention=>Experience focus

It might be obvious, but I hadn't seen it written down as simple as that anywhere.