Hulu is basically a repository of all the officially available streaming videos online. Thus, if you see a video on Hulu it is because it was available on the studio or network's web site at one time. In some cases the videos are no longer available on the official sites, but the studios and networks often use Hulu as an archive/hosting service to keep the older content available. This is especially the case when the studio or network has no plans for selling a DVD of the film/show. The reverse is also true: if you don't find a video on Hulu, it is because it is not available on the official network or studio web site.