One standardised storage format for common data

Is it too much to ask for software developers to agree on one standard storage format for commonly accessed data?  Why does every browser that I use have it’s own bookmarking system, rather than one location separated out from the actual programme that all programmes can then access.

For example, Firefox keeps it’s bookmarks at …/.mozilla/firefox/…default/… (different for each OS), Flock does the same in it’s own location, and so does Chromium.  Why not have one bookmark storage standard that gets kept in /home/michael/.bookmarks?  Every browser can then access the same place and so will all have the same History and Bookmarks, no matter which browser I’m using.  The same is applicable for RSS feeds.  Why can’t every application use a storage container that’s kept in /home/michael/.rss?  I’m hazy on the details, but I thought that this was the sort of thing that XML was designed for?

The Akonadi framework on KDE is going to go some way to address this problem, but only within the KDE desktop, and only for the (personal information management) PIM applications.  Am I missing something here?  If you know of a way to share resources across applications, please point me in the right direction.