question: difference between DefaultKeychain and Basic struct

[harrypunk]

I found that DefaultKeychain and Basic both copy the values of username and password. DefaultKeychain merely decode base64 string first.
keychain.go#L172

        return FromConfig(AuthConfig{
		Username:      cfg.Username,
		Password:      cfg.Password,
		Auth:          cfg.Auth,
		IdentityToken: cfg.IdentityToken,
		RegistryToken: cfg.RegistryToken,
	}), nil

basic.go#L24

	return &AuthConfig{
		Username: b.Username,
		Password: b.Password,
	}, nil

Is the bas64 decoding the only difference between them (when other 3 fileds are empty)?