omg. This might well end in a flamewar so I will not post in this thread after this post - no matter what you will say.
Yes, I do think before typing. And I am astonished how many people believe this shit (as apprarently you do).
Duping an item offline (ie. changing you local savegame or changing the gamestate while ingame) has NOTHING to do with the dupes of items online. Why would you even care if somebody is running around with all the best items in his offline game? Even in D2 he could never join an online (battle.net) game with this character. In fact all battle.net characters, items and games were just as much serverside as everything in d3 is. So d3 is about as "dupe proof" as d2 battle.net was (disregarding small improvements in their item management for the moment).
All they did was REMOVE features. The battle.net gameplay (which is the only one left) is absolutely uninfluenced by this change!
To clarify it once more: yes, when you are on their servers they can monitor you. So the right choice was made for d2: either you are online with that character for every game and everything is stored on their servers or you can only play offline / lan - in which case nobody cares whether you cheat. These two worlds never interacted. If you think the offline mode was the reason for the dupes to exist you must be among the stupidest persons i've ever met. (At least initial dupes usually involved two or more characters picking up an item "at the same moment" by creating laggs or similar mechanism that involve tricking the server, which cannot even be tested or recreated offline!)
Maybe you should start to think - not necessarily before opening your mouth, but rather after somebody (like Blizzard) told you something and decide for yourself whether that makes any sense at all.
P.S.: yes, I meant activision. It's not like that changes anything.