@Alan
Well, the "bookmark" is my experience with webapps.
All the webapps that I daily use are nothing more than bookmarks
(gmail, dict, OSM, Amazon, tumblr, various games, ecc) and often the
websites themselves say that I should use the native app for Android
instead of going to the website ;)
All the other features that you are mentioning sound definitely
interesting, but none of them are useful to me now, nor I have seen
them yet anywhere in my daily experience.
So, why should I use a webapp instead of going to the website? The
only reason that I have in my daily experience is because it is a nice
bookmark.
Davide Alberelli