Many skills from WoW seem to take their cues from Diablo 2. WoW Paladins have D2 Paladin skills such as Holy Shield and Holy Bolt nearly intact with slight name and mechanic changes, and many of their Auras are slightly renamed and retooled versions of D2 Paladin Auras. Warriors take a bit from from the Barbarian class with Whirlwind and their battle shouts. WoW's talent system itself seems to be very closely relate to D2's skill trees - but with wise modifications such as the ability to respec, and making most abilities available by default.
Even later revamps and additions have in part taken clear cues from Diablo 2. Seal of Blood is very similar to a Diablo 2 Paladin's Sacrifice ability, and the Death Knight's Corpse Explosion is one of the Diablo 2 Necromancer's trademark moves, while Warriors will be gaining the Barbarian ability to dual wield two handed weapons. Diablo 2's socket system was also modified for WoW with the Burning Crusade.
Is this a bad thing? I don't think so. WoW itself, as a game, was built on looking back on the MMORPG genre, taking aspects of what came before it in games like Everquest, and making it better, making these abilities its own. It's not too much of a stretch then to imagine it taking strength of other previous Blizzard games, and it's likely a better game for it
What looks to be interesting too, is that Diablo 3 itself may be taking at least some cues from World of Warcraft. The discussion of a "respec" ability is probably tied to being able to respec talents in WoW. Similarly, the new ability to use multiple skill hotkeys may have been inspired by WoW's hotkey bars. I know I'll probably be watching for more WoW inspiration as we hear more about the game.
It may seem "unoriginal" at first glance, but I think taking best practices like this can only serve to strengthen both games, and make a better playing experience for all Blizzard gaming fans. Who knows - maybe some of Diablo 3's innovations will be making World of Warcraft's future expansions better as well.