Those mechanics aren't used as heavily as they are in Northrend, but they most certainly are there in the old world. Every single zone has received some sort of attention in Cataclysm, and many zones have received complete rebuilds from the ground up. Every zone is much closer to being in line with Blizzard's quest design of 2010 rather than the design of 2004.
TAD also asked:
"What's the story impetus now for players to even bother going to Outland or WotLK?"
Outland and Northrend are in very strange places now that they've revamped the "old" world in Cataclysm. There's an immense disconnect in the story between levels 58 and 78 now. The quests you do in those areas technically take place in the past as far as the story goes, and you just have to roll with it and pretend it's perfectly normal. There's very little story impetus. None at all, really. It's just a victim of the fact that Blizzard is already rebuilding most of the world, they can't rebuild another at the same time. Maybe next expansion will see an Outland revamp that sets the story right. I won't lie, I loved Outland. Most people didn't, but I did. Zangarmarsh remains my favorite zone in the game even after seeing the Cataclysm beta. I'd love a reason to go back there.
"With Darkshore and Auberdine destroyed in Cataclysm, how do the draenei and the night elves get from their islands to Kalimdor?"
The night elves still have an encampment in Darkshore. After Auberdine's destruction, they moved further north. To actually answer your question though, you sail into Rut'Theran now, off the coast of Darnassus. Then you take a flight down to Darkshore.
"You know the thing where you complete a quest, and you can turn it in right there and get the next quest instead of going back to the quest giver? Does anyone know if that has been implemented for BC and Wrath content?"
I think people are misunderstanding this feature. Not every quest gets that treatment. Not every single quest completes automatically in the field and lets you pick up the new one in the middle of nowhere. This is only for specific quests and quest chains. The Burning Crusade and Wrath of the Lich King's content has been touched very little, so you most likely will not be seeing that in any quests in those areas. Only very specific parts of the new Cataclysm content have received it.
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