I guess you never played HC.
One of the biggest problems with HC mode in D2 were Town Portal PK's that used a 3rd party program. Basically what it did was fire projectiles like Ice bolt or hydra, open a portal, to town, and activate hostility. It would do this so fast that often you wouldn't have a chance to react and would die almost instantly in 1-2 hits because they were twink geared for killing you and only you. So this caused the "chicken" 3rd party program, where you could exit the game with a one button press as soon as a portal went up.
TPPK made playing HC in public a royal pain in the ass, so basically you had to find a trustworthy group or go it solo. Many times people would befriend you for a few games, then kill you once your guard was down. I know it took me many painful deaths and item losses to learn that. Still, once i found a good group of players, the challenge and split-second intensity where one wrong step means losing it all made for some awesome HC memories.
Anyway I don't expect D3 to have these exploits since it's arena only.