When you purchase a quality video (Usually the more expensive ones) then you not only get the method (and the rights to perform it), but you also get the creator's thinking and tips.
Not to mention it's basically very lame to just see someone else do a trick and then copy it without some form of compensation or chatting with the creator you saw. When someone creates a trick they are developing intellectual property. To then duplicate their work is often seen as stealing that intellectual property. They thought of it first, and if you like it you should do something to make sure you're in the right in performing it - as in, either buy it, or ask them if they are OK with you performing it.
As an example I was at a convention this weekend and saw a routine that blew me away it was so beautiful. It was during a lecture. Even though he was teaching these things to us, I still went up to him to ask him if he would mind if I used that routine at an event I'm attending in May.
