Possibly Blizzard decided that hunter's didn't have enough of a bad rep in groups so thought they'd help things along a bit

I think if you turn off the option which causes the auto-target thing it leads to a dps drop (there is a reason but as hunter isn't my main I wasn't paying attention when I read that) which may explain why some hunters leave it on despite the add pulling potential. For 'solo' play though it's probably more of a gain to turn it off and know that you won't get any surprise mobs heading your way.