Asymmetric encryption in WS-Security spec.?

[Christof Soehngen <Ch...@SYRACOM.DE>]

Hello,
 
does anyone know, why the WS-Security specification does not allow asymmetric encryption.
I do understand that it is not as fast as symmetric encryption but _for small messages_ does the following hold true?
enc_symmetric(message) + enc_asymmetric(symmetric_key) < enc_asymmetric(message)
 
Especially if you want to sign _and_ encrypt every message, one asymmetric key sounds more efficient to me (RSA should be able to do this, DSA should not, as I understand from what Werner told me).
 
Thanks,
Christof