When I was bootstrapping my startup while working a day job, I used to wonder how to answer that question. My product was bringing in more money then the company's costs, so it felt "profitable", yet not enough to employ me full-time. Seems like there is a difference between that and something that is just plain unprofitable (where the burn rate will eventually cause the bank account to go to zero).
The software doesn't write and maintain itself. So if the revenue can't cover the expense to write/maintain the codebase (i.e., dev salaries), then the app isn't profitable because one of the major costs can't be met out of revenue at 100%.
