The quintessential quick dagger
Rogues love quick weapons in their off hand for a variety of reasons, many of which have changed from expansion to expansion. Currently, Deadly Poison's insane potency and percentage-based proc mechanics make every rogue spec value a quick weapon to apply it with. Combat rogues are enjoying Combat Potency procs, while assassination rogues' poison application chance literally demands tons of Deadly Poison procs to function. Subtlety rogues can't do any better than Deadly Poison either, and so they're looking out for quick off-hand weapons too.
The catch is that Blizzard's team has yet to implement any quick off-hand weapons that aren't daggers. There are no quick maces, swords, axes, or fists; they can't be crafted, and they can't be found. If you're a rogue, you want a quick dagger in your off hand, laden with Deadly Poison. There's no spec dependency or variation -- you need a quick dagger. Luckily, there's one available from the justice points vendor for a song and a dance, but the fact remains that it's required. It's not even a matter of a not-quite-so-fast axe or sword versus a very quick dagger; the non-daggers are so slow that they simply cannot work. You can't play a rogue effectively without a quick dagger gracing your weaker hand.
The heavy-hitting main hand
Mutilate rogues used to be hand-agnostic, not really caring about the speed of their second dagger or its location. Obviously, they needed one quick dagger, but the other was a toss-up. Here's where the combat tree gets its revenge on assassination for being forced into wielding a dagger. Mutilate rogues now depend on Backstab for the crucial 35% execution phase of each encounter, and Backstab is decidedly not speed-agnostic. Assassination rogues now want a slow main-hand weapon capable of huge Backstab crits, aligning them with combat's preferences.
Combat rogues still obviously want a slow MH weapon to deal more damage with Sinister Strike and Killing Spree. The speed of the MH will actually be even more important in 4.0.6, as Blizzard's devs are fixing combat's (awful) mastery bonus. When Main Gauche starts using our MH weapon to calculate its damage, having the slowest MH possible will become even more key than it is today. Don't worry, it's easy to get a slow axe/sword/mace/fist; there's not a single quick one in the game to clog up your loot tables.
Hunters win this round
I'm sorry, I really am. We're going to have to stop rolling on guns and bows, no matter how much we enjoy making hunters pay for stealing our gear. Deadly Throw has never been very great outside of PvP, and even then, it's been really weak since the DT interrupt bonus was removed from our PvP gloves. Redirect would've been so sweet to use with an interrupting DT and could've really showcased some of the amazing skill that the top-end arena rogues display. Deadly Throw is still only mediocre, and it was the only item tying us to a thrown weapon.
The new Fan of Knives changes all that. Now, in order to use our most potent (well, only) AoE ability, we have to have a throwing weapon equipped. With the importance of Fan of Knives on so many encounters, there's really no reason for us to use a gun or bow if we can help it. I know that the item developers didn't include a lot of thrown weapons, and as such, they're pretty sparse. I know a lot of rogues who have been picking up the PvP throwing weapons because they simply haven't found anything else. With so few thrown weapons in the game, you don't really have to bother choosing between speeds or stats; your job is to be happy with what you have.
Parity amongst the specs
If you're a rogue, you want a slow main-hand weapon of your preferred weapon type, a quick off-hand dagger, and whatever throwing weapon you can get your hands on. The universalization of the quick off-hand dagger makes it incredibly easy for rogues to switch between specs on the fly. With these speedy daggers readily available, you can half the most important part of your arsenal set in no time.
While I lament the extinction of combat off-hand weapons, I have to agree that it's pretty nice to be able to switch to combat any time I score a slow main-hand. All of you rogues who said that we weren't really rogues without daggers have had your wish granted. Well, half of it, anyway.
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