It's a chicken-egg issue. Content requires users, which requires content.
Ideally, questions are those problems that we are actually dealing with at work today. The primary goal of Stack Exchange is to make the internet a better place - no small task. The niche it decided to fill is that of expert problem solving; specifically making it easier to put a question in a given topic in a venue where it can be answered by an expert, preferably multiple experts with multiple approaches. This is true across all the SE sites.
There's only one of the two aspects of that that we have control over: providing the expert answers. We can't force anyone to ask questions. For that, we can only indirectly influence the incoming questions with advertising and publicity.
These aren't complete thoughts, I realize. I'm trying to get a development project wrapped up so I don't have to come in this weekend :) I hope to update this with some more thoughts, but this is the start of what I have in my mind.