McNastea has it right: the whole point here is to balance parry with shield users. It is very clear to me that parry was a better way to build a character than shield before the new change. It seems better balanced now but, like Araël, I'm not sure parry is not, still, superior to shield.
At least it is debattable now.
I've got plenty of both types of tanks, and I honestly don't prefer one to the other. Sword and board has a few nice things going for it that people are quick to discount: Shields have a lot of nice bonuses, shields allow you to block ranged attacks, your ab stays higher, your damage is higher, you can wield a larger weapon - and most of the best weapons are bastard swords/long swords. You also get to hang on to a TON of feats and you can put your skill points elsewhere.
Two Extra attacks per round, 1.0x + 0.5x STR modifier, 100% Damage Modifier on Off-hand weapon, 1d6 weapon have often 18/20 threat range
I'd argue that most dual-wielders are only going to get one extra attack per round, since most of them aren't fighters so much as rogues and the like. This is true of all of mine, at least. And the STR modifier thing is negligible since, as I said before, most dual-wielders don't really have much in the way of str.
All things being equal, I still prefer to tank as sword-and-board because
that's what they're meant for. More likely to hit enemies while tanking, more likely to stay in the fight longer due to being able to block ranged and having a larger hp pool to work from. I loathe having to tank things on Edwin because he has to whittle enemies down 5 hp at a time. If I had a tank with me and I could flank, it'd be much easier.