If you watch the video, on the first fight the monk doesn't have a mantra up. There are parts that the monk rushes into a pack of mobs and dies (while having an offensive mantra). These builds may not be viable for HC. When I watch this video, I get a feeling they want to satisfy people that kept saying d3 is too easy. I think it will take months to beat inferno on HC. I mean even in d2, if you played HC and started with nothing, it would take a lot of hours to beat the game comfortably. Especially if you take out the potions, portals, and exiting the game.
Plus, I am sure they will adjust the difficulty after release to make sure the game is enjoyable and challenging for HC players.