First of all, it is entirely possible to patent magic tricks. See, for example, U.S. Patent #'s:
5,354,238 -- a method of simulating levitation invented by John Gaughan (review this the next time you see David Copperfield soaring)
6,174,241 -- Mark Setteducati's Magic Book
5,409,420 and 5,445,565 -- two more inventions by Mark Setteducati
5,605,508 -- a guillotine by Alan Wakeling
4,565,364; 5,551,921; 5,549,515 -- assorted Tenyo patents
5,886,956 -- Lubor Fiedler's Phantom Clock from Tenyo
These were found with only a few minutes searching on the US Patent Office Database -- there must be more.
The argument that "Patents are expensive" is true. So what? If you aren't willing to take available steps to assert your rights to your creativity, then don't complain if someone else uses your work. If you invent something and put it into the marketplace (even the small magic community) without patenting it, you are placing it into public domain, and you lose your rights. That is settled law. It seems unethical to me for a magician to call those who use public domain materials a "thief".
Yes, you must disclose the method to get a patent. Again, so what?? This is just like hiding an effect by publishing it in a book. How many lay people at Copperfield's show think, "I bet I can find the method to flying by going to the Patent Office's database"?? zip, zero, none
Geno Munari claims the rights to Page's routine. Fine, I'll grant that magic works better and is advanced as an art form if we as a group respect signature acts. But what is a routine? how much patter must I change before I've made it mine? What if I drop one of three phases, and insert a new one of my own invention? Is the routine 2/3rds Page's then? Because routines cannot be objectively quantified, arguments about their ownership will always be just that -- arguments. The good magicians will either creat their own routines, or take existing work and personalize it until it is their own. Jamy Ian Swiss said it best in a Genii book review a couple years back -- the best reason not to steal a routine is not that it is ethically bad, but that it is theatrically bad.
From Jim Riser: "Bob Keyser does own the legal trademarks for P&L items. Therefore, he owns the rights to the P&L Cups." What Keyser most likely owns is the right to use the P&L name and hallmark in association with cups (or other magic items). Your own web page shows that the basic design and salient features of the P&L cup predate Petrie and Lewis by some time -- their cups, while optimized and refined, aren't new.
Likewise, the most Busby can claim on PF cups is the right to use the Paul Fox name and logo, not their basic design.
Another point -- in, most of the spats I see about who is stealing what, the one making the accusations is asserting his right to _someone else's_ creativity. Not always, but often. This seems odd as well.