However it's much easier to get users if you do have a business plan, or as I prefer to think of it, a business model. If you throw something out there on the internet and start gaining users, you probably have more of a plan (model) than you think.

Having just a good business model can generate sales too though. Actually there's quite an argument for doing so before writing any code. Its a whole lot easier to change some words around on a word document than to completely rewrite an application.