inDinero has what, five employees?
As teams grow and the scope of what they do grows, the need for specialization also grows.
Let's assume a wonderful team of world-class engineers who all happen to have the same skills as a world-class product manager, and who all like product management work. (If you like, they can all also be world-class designers.)
In my experience, pure product management work grows pretty linearly with the number of developers. (Providing they're organized, more developers means more projects or increased velocity on existing projects. Either means more product work.)
In this situation, each developer could spend X% of his time on product management work. (Let's say X% = 10%, since in my experience one product manager can keep ten developers busy.)
Great, you might think. Since every one of these developers can do and likes to do product management work, they'll each devote 10% of their time to it, and everything will work out fine.
There's only one problem with that - great products aren't built in small isolated portions. In order to be an effective product manager, you've got to know the whole product - so everyone doing any sort of product work has to coordinate with each other. As the team grows, so does the coordination overhead.
Even assuming a perfect central repository of knowledge (an uber-wiki?), so each developer only has to do a knowledge dump once, just consuming and synthesizing all the information created by all other people takes an increasing amount of time. And then there's the need to reach consensus when people's syntheses disagree, as they invariably do.
In these situations, as the team grows and/or the product gets more complex, someone inevitably ends up spending an increasing amount of their time on product, while others stop spending any. Someone becomes the guy who makes product decisions, while others defer to that guy.
Perhaps, when the dev team is ten people or so, that product-focused person's still spending a bit of time coding, and still calls himself a developer. But as the team grows, it's inevitable - you will either hire external dedicated product managers or you will grow them yourself from the inside.