What you say makes sense when you're selling a product. With most of these applications, their potential money making product though is the back-office data they collect on the users themselves which they then sell to brokers or data warehousing services, or provide to targeting advertisement firms. From that stand point you simply want the largest installed user base you can get.

A successful smart phone app based on these metrics is the one with the largest user base. You get that user base by providing a simple to use product that quickly addresses a need for the largest number of people, rich, poor, white, black, etc...

Now, if you're talking about targeted applications like certain types of gaming apps. Or apps that provide an extended retail experience? This is when you talk about focused demographics.