VHS recordings of live TV are a bit different. According to Sony Corp. of America v. Universal City Studios, Inc., this practice is known as Time Shifting, which is simply making the recording available for later use. The ad money has already exchanged hands, and the work was already available for public use. The court rules 5-4 that this time shifting fell under fair use.
YouTube ad money works a bit differently, and downloading the video tends to bypass that process. Also, Streaming is by its nature on-demand, so there are a lot fewer benefits for downloading the video. Furthermore, U.S. copyright law has changed since the previously cited case, so there are some extra restrictions to contend with that the Sony case did not.