I made Storybook (number 2 on the blog post) with my brother. It's an HTML5 app that can be packaged with Phonegap, although I'd need to use the Facebook phonegap plugin rather than the standard Facebook authentication. I think HTML5 apps can be developed faster, but the integrated stack (especially of iOS development) can accelerate development. Also, there are many more mobile developers using the native SDKs than Phonegap, even if Phonegap apps could be built faster (but they might not be the same quality. Phonegap apps often aren't tailored to the platform, and HTML5 apps very often feel and look different than native apps, even if they can appear native, like cheeaun's HN mobile web app)

Mobile and web development are different and have different mindsets. For example, mobile apps require a separation between the server and client - if you want to communicate with your server, you need to make an internal API instead of directly running SQL/MongoDB/etc calls. Also, in a mobile app, users may not have a data/internet connection, so developers need to implement persistant storage on user's devices to work offline. At this hackathon, it was about half mobile (maybe more) and half web.