Signing without encryption is worse than useless by providing a false sense of security (see e.g. http://th.informatik.uni-mannheim.de/people/lucks/HashCollisio

Signing without encryption is worse than useless by providing a false sense of security (see e.g. http://th.informatik.uni-mannheim.de/people/lucks/HashCollisions/ http://th.informatik.uni-mannheim.de/people/lucks/HashCollis... , MD5 used as an example); and costs to start signing are virtually identical to encrypt-and-sign (not just financial costs to providers: most of all time-and-effort for everyone, including users).