The fact that operas get filmed and released on DVD all of the time is why I find the "live experience" argument so dubious. Of course theatre is best experienced live, but if there's no possible way you can ever see a show, it's better than absolutely nothing.
Btw, a lot of operas get turned into movies: Madama Butterfly, Die Zauberflote, etc. So, yes, they would risk losing revenue for movie releases.
For instance: when I saw Avenue Q on tour recently, a girl behind me was telling her friend that she wanted to see Legally Blonde when it came here becaus she had seen the MTV broadcast and it was really good. And, judging from her other comments, this was not a hardcore theatre junkie.
Jimmy, what are you doing here in the middle of the night? It's almost 9 PM!