I'm wondering if anyone is still using the username/password web service authentication, also known as "simple" authentication ?
The username/password web service authentication is intended for integration with student information systems or other enterprise software: http://docs.moodle.org/dev/External_services_security#Simplified_web_services.
With the token ws authentication you can do everything. With the username/password ws authentication you can not make a call as a web user. Moreover there are known issues with the username/password ws authentication as: no JSON support, no download support, no upload support...
I would prefer to see Moodle dev focussed on polishing the token authentication and developping a cool oauth (2?) authentication, than fixing the simple authentication which seem redundant anyway.