I think the hang up is that Blizzard seems very bent on giving players a sense of progression through the leveling process. And if I'm being honest with myself, I genuinely support that even if it means F2P have less content to engage with. From a story telling perspective it makes sense.
It's the reason you cant deal with the world affecting questlines of Blackrock Mountain and its various raids until you deal with the local threats of the Defias or Lord Godfrey. As a progressive narrative, it just makes sense.
What I would like to see (and I think is coming in a few xpacs) is setting up pre-req quest lines. So you can go adventure in STV when you hit lvl 30 if you want. But if you complete the questlines in Duskwood that breadcrumb to STV, you can unlock STV regardless of what level you are. And if, while leveling in STV, you hit 40, you can choose to go to Badlands. OR you can complete all the quests in Loch Modan/Wetlands that kinda set up the Uldaman dungeon and you unlock the Badlands, even if your level 20.