Demographics aside, one of the most compelling factor in making your decision is your available resources (assuming a web app can support the desired feature set). If you are building a desktop app you have take into consideration the fact that you will only have access to customers who's operating systems you can afford to support. Take into considerations OS updates, hardware specific issues, and software interactions. If you build a web application you only have to worry about the self contain environment of your server, and browser support. So if you have enough developers to overcome the issues associated with a desktop app then go for it.