The thing is, you really have to go out of your way in order to learn magic. Most people do have access to learning these tricks, but never look them up.
Here is an example: I had a teacher in my high school for 3 years, and every friday he did a magic trick for the class. Every single time we were amazed. I learn now that all of his magic was a series of double lifts, deck set-ups with false cuts and shuffles, and forces. I didn't know that for 3 years, yet it was at my fingertips the entire time with a simple youtube search. It took me wanting to perform these tricks in order to learn how to do them.
I am going to school to be a teacher as well (accepted into Penn State's college of education, graduate '11) and i plan to perform a card trick every friday as well. I am not worried in the least bit about someone knowing these tricks, or finding out how to do them. I say this because it is all about presentation. Even knowing the tricks i still get surprised by their performances.
Even if i run into one of the ten thousand magicians out there, they will not reveal my secrets because that would ruin their routine as well.
Also, if the "double lift" were given away to my class, there are so many ways to get around that, because it can work to your advantage. They only know that move, and look for that move specifically, so doing a trick with another sleight, or a double and then another sleight, will completely throw them off. If you look for something thats not there, it is so hard to catch anything else thats going on. Knowing one and not all sleights can actually distract the viewer.
And that would be worst case scenerio.