okay, i noticed everytime the new trailer (french) is up the authors claimed about the video rights and stuff but isn't normally when you tape it 'your video', so why do they keep doing that :(

I don't understand lawyers and all their rules.

But you've got to understand that it is footage owned by them, whether someone else records it or not. I can't give you a good reason for them wanting to delete it, but obviously it's a marketing strategy. The music companies do it all the time, even if only 5 seconds of their song is used in a video, they still have the rights to get a youtube administrator to take it down.

My only guess as to why they would delete the trailer is to get you so hyped up (without any spoiler footage or extra scenes) that you wanna see NM even more than you did before (meaning another fan buying tickets, equalling more money). It's very stupid when you think about it, but obviously it works when you look at it from a business angle, or else they wouldn't be doing it.
Do I agree with their methods? No. Do I think they're greedy jerks? Yes. Anyways, there's nothing you can do except watch the vids before someone flags them and they get deleted :/