How much influence do they have in getting dvd's released, and do they really contact the respective studios? I mean what about one hit wonders? Do they still have contact details for early or not so popular tv shows?

They really contact the respective studios, and have contact details for those shows, but they don't have that much influence in releases. They can persuade studios to release a certain title or continue with a certain series, but they don't have leeway on guaranteeing those things happen.