What extra features has the Android Youtube application over the HTML one?
You shouldn't lose any viewing features. The YouTube application is simply a way to make it easier to view and search, without having to load the entire html pages. Probably the only feature you wouldn't be able to take advantage of (and i don't know this for sure) is uploading. You can use the YouTube app to upload videos you've taken to your own YouTube account. And like i said, you might be able to do this through the browser, but the app is just a way to make it easier. Simplification is key.