I imagine the people Nintendo want to stop most are the commercial pirates not the people who download games at home.
I recently bought a copy of Professor Layton from ebay as there weren't any available in the shops. I was somewhat annoyed to discover I had bought a counterfeit copy despite avoiding all the cartidge only and despatched from hong kong auctions.
Still if they had shipped enough games to keep up with demand I would have bought it from amazon and avoided flea-bay like the plague as I usually do.