Basically, I think xdg-utils from Freedesktop is doing what LSB Desktop should have been.
LSB wants distributions to provide a set of binary API (gtk2, qt3, now also qt4...). I don’t think that’s what vendors need.
Freedesktop provides a set of commands, providing a set of features with very simple API, allowing to easily integrate in any distribution and desktop environment (not even only under Linux).
Distributing the libraries with your application is easy (I think LSB can make sense for things like libc, etc). What vendors want is to integrate with the distribution (appear in the user menu, be associated with mimetypes, be able to start a browser, disable screensaver while the play a movie, get proxy configuration, maybe send an email...) without writing much code.
Freedesktop doesn’t mandate distributions to keep obsolete unmaintained libraries, it just asks them to provide a set of simple commands implementing the features in any way they may desire.
xdg-utils is now required by LSB 4.1 and that’s a good thing, but I believe most vendors are just interested in it, not in the rest of LSB.