I think that was just for this build.
I don't think MS ever put up 10.061 ISO, so methinks they decided to just skip that and let everyone on 10.074 - their showcase PB rls for the developer conference.
I have heard that 10130 will be made available to the slow ring and therefore also as an ISO file for download. Does anyone have any insight as to when this might happen? I'd like to try an 8.1 to 10 upgrade...