There are anti-dupe mechanisms in place, but Blizzard knows they'll eventually be overcome
Duping is biggest concern here, especially since offline/online characters are mixed. If there are no measures essentually you wont be able to play online. As soon as you join a game you have people with insane duped gear spoiling all fun. As soon as you try to trade you will receive ton of duped freebie items probably for free even. And playing offline only is taking half of game away.
Now we know that there is a mechanism, perhaps save file encryption. Second part of sentance suggests that Blizz will not advance this protection when eventually save files are eddited. Which is fair enough. Real question is how long will it take? The longer the game is dupe free the more enjoyment I will get out of it.