First and foremost, suspend your disbelief with resurrection. If we didn't have it, then we'd have permadeath, and that would be hell. Seriously, it'd be the worst thing to ever happen to any game, ever.
But, given the necessity of it, let's take a look from a lore perspective. Warcraft lore itself is based off of the plethora of myths, religions, and other stories which comprise the foundation of western thought (although there is certainly a lot of eastern philosophy included as well). Resurrection in the western world, while physically impossible for human beings (queue some BSG music) right now, it is a generally accepted metaphysical principle. You don't necessarily need to believe you can be resurrected after getting a sword stabbed through your heart, but the concept is not a shocking or unfamiliar one.
Thus, resurrection is part of our collective understanding as a people -- whether or not you think resurrection is possible or not is unimportant; it is understood and thus makes a good element to include in a video game where such things, which are not common place in reality, are common place in Azeroth. Given the underpinnings of why WoW, and other games, include resurrection, it's not hard to say that every day players are able to resurrect people, lore wise, because of their metaphysical connection to gods and the greater world.
Who wouldn't want to be able to bring back from death a loved one? There might be arguments if such a thing should be done, but at the end of the day, I'd do it in a heartbeat.
Thus, players are put in a position of having such power. Their ties to the gods of Azeroth allow them to function as their super-natural vessels, bringing forth life to which it was prematurely taken from. It doesn't matter if you're level 1 or level 85, you still have that tie to the gods, and at the time they see fit, you get part of their power to give life.
"When Cataclysm hits, do you think non-DK's will be able to fly into Archeus?"
I would assume so, although it's just an assumption since we don't know for sure.
"Will we ever be able to send gold across factions? I'm sick of losing 1000g+ every time I want my Hordie to have some cash. A mailbox in a goblin city with a neutral AH would be great. Maybe even with a fee. Sending heirlooms across factions is possible, why not gold?"
I admit it would be nice, really nice. It's obvious that the technology is there to send things across factions, but there are artificial limitations in place that prevent this (sans heirlooms). Blizzard could, technically, allow gold to be sent across factions one day, but we haven't seen any indication that they're going to let us do it.
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