well web app is already built, and the Kickstarter's for native mobile app. no need to use the web app if you don't want to.
But the reason I chose web first is (1) easy access to all platforms, (2) plug into web services and hooks. Eg, there's the Chrome extension (http://goo.gl/gze94) where you lose HP for surfing reddit, facebook, etc. Pomodoro plugin, and future integration with Pivotal, Asana, etc. Integration is easier on the web.