No idea the relative likelihood of these options, but here's the option they're worried about: 3. If a non-subscriber wants to watch the show, they will go with a free option if available instead of becoming a subscriber.

Microsoft benefits greatly from having a healthy ecosystem of 3rd party companies developing on their platform. It is not their goal to crush these. In fact, Norton's awesome applications were a big part of Window's early success. (Note, this is different from the web browser where having control of the default home page is a valuable advertising surface.) Microsoft isn't trying to sell anti-virus software. It is included free with Windows. The only reason they started developing anti-virus software is because the 3rd party stuff sucks so bad. It used to be good. I'm not sure what happened. Maybe viruses because more sophisticated and these companies just couldn't figure out good ways of detecting them. Maybe these companies started using hostile marketing techniques that turned people off to them and led to more unprotected machines.