I think these "rules" on when to coin or not are pretty bogus. I sometimes coin out a 2 drop without a 2 drop follow up on turn 2. Sometimes in constructed I coin hero power on turn 1, especially if I have an autobarber in hand and I expect my opponent to drop a 2hp minion.
Part of the point it to use every single resource available. And since rogue's hero power sticks with you, I think its perfectly fine to coin out a minion on turn 1 and hero power turn 2. Also, it really just depends on the match up and your long term plan to win. Most of the time I do agree that there is no point to coining a minion out and then hero powering. Although I'd imagine sometimes your plan changes from turn 1 to turn 2.
Another instance is with shaman. Getting a haunted creeper out on turn 1 and then hero power turn 2 is fine imo.
My favorite thing as shamen is to coin whirling zap o matic, if they can't deal with it its so strong. Especially with a taunt totem or removal to kill a non-charge minion of theirs.