There’s nothing wrong with developing a mobile website instead of a mobile app. You have to create the right tool for your audience. There may be some ways you can tweak your site so it acts more like an app:
As smartphone sales continue to soar, more and more developers are focusing their efforts on building applications for mobile devices. Whether it is a native application or a mobile-optimized website, mobile innovation is taking place at a breakneck pace.
via HOW TO: Make Your Mobile Websites Act More Like Native Apps.
It’s up to you how much functionality you need.