If you think "build it and they will come" applies in the mobile space, you're completely wrong and about to light a bunch money on fire. I'd be very interested to know if this team talked to 25+ people smack in the middle of their target audience about their expense-tracking pains before starting to think about building the app. It really seems like they thought of a problem (or what they perceived as a problem) and then built the app. If they dove deep on the problem and talked directly to people who they thought would most benefit from the app, they certainly would have uncovered more information about why Birdly would or would not work for them and could make important product choices based on that feedback.