Once again DW has come up as the quick fix for ret paladins. It really wouldn't fix anything. Why do people think it would? DW by itself isn't all that amazing.
Rogues are intended to be the highest DPS class and they DW, but they have no support abilities. When you give almost nothing to your group and you are in close range of mobs, you'd better do some pretty amazing damage.
Warriors aren't exactly a great record either. Fury does more personal DPS, but in larger raids the benefits of Blood Frenzy in arms become significant enough that raids with high physical damage should run with an arms warrior.
Shamans? Well sure we got a huge damage and support boost in TBC, but is it really because of DW? We already had a 31 point talent. Between a new talent there and DW spec, we ended up with four extra points. In addition, Nature's Guidance ended up looking like a necessity, so that's 13 more points in resto.
What if we still used 2h weapons? I imagine the standard DPS build might end up something like this:
With mental quickness shocks become a more significant portion of our DPS. Reducing the cooldown and increasing the damage would be a big help. Searing totem would benefit well from the buff. Elemental devastation is mostly noobish speculation, but with more shock-spamming it could end up being beneficial. And who knows, if Blizzard wasn't figuring out DW, maybe they'd have made enhancement and elemental synergize more.
But let's get back to paladins and DW. Blizzard clearly wants to collapse gear. We want them to as well. It sucks to kill a boss and end up with crap because every spec and class needs different stats or at least stat ratios. Everyone wins when we can share gear. And no, this isn't a socialist pipe dream, it's us getting gear more easily and Blizzard having to do less work. Think of it as moving from hand-crafting to factories. Ignore all the Marxian jib-jab about separating the worker from his product...
So what's the benefit of moving paladins and warriors entirely to +hit plate? Nothing. It means redesigning ret, again, and for what benefit? That work could be put into making work better what we have already. Arms warriors certainly don't benefit, unless arms is going to be changed into a DW tree, creating even more work, or it will get completely screwed for gear. Fury doesn't benefit since it doesn't need loads of +hit anyway. Yes it has a very high hard hit cap, but diminishing returns set in very fast; once yellow damage is hit capped they benefit more from AP and crit.
Giving paladins DW would only create a ton more work for the devs, possibly screw up arms, not help fury at all, and isn't even guaranteed to bring any benefit. DW is not the cure-all. Talents are critical and DW is only one of many possibilities, a weak fix.