At present, warrior mechanics are designed so that, at low or no rage, warriors perform worse than other classes. Warriors need to either take or deal damage to gain access to their 'fuel' so to speak, and their various stances and abilities are designed around that mechanic. (While another tank shares rage as a tanking mechanic it doesn't share stance switching, druids are expected/designed to stay in bear to tank.) Combining this factor with the various warrior sacred cows (the five stack of sunder on a target a protection warrior provides himself while tanking it, the 50% healing debuff an arms warrior provides, the ridiculously out of control semi-AoE of glyphed Cleave and Whirlwind for fury) and what we have is a class that is baseline undertuned, but has the ability thanks to rage and abilities that exploit rage to, effectively, 'overclock' itself.
Do a DPS parse on a fury warrior on a typical five man. Watch his DPS on trash, and on bosses. On a single target DPS fight, the fury warrior will hover at or below other hybrid classes in terms of pure DPS, depending on how creative he or she is with his or her abilities (rend dancing, for instance): they're certainly not more potent and may even come off as less so. Now, introduce trash mobs. The fury warrior's DPS goes up. Now, introduce waves of constantly spawning trash mobs, and a sustained damage mechanic that keeps rage bars full. Watch the fury warrior go. With limitless rage and the ability to make near constant use of Cleave and Whirlwind on a steady stream of adds, even a mediocre DPS warrior can put out ridiculously high DPS. This is a problem for class balance, and it's one I've mentioned before. Rebalancing Whirlwind to be a true AoE and making Cleave a button that requires real decision making, this isn't a bad change by itself.
The problem lies in the low DPS when not using those abilities. A DPS warrior pulling 9k or more on a run can often be seen to be doing half of that or less on a boss, especially one with a lot of motion or no steady rage return mechanic. The warrior DPS cycle is feast or famine. It's not harder than other DPS rotations (it's certainly not harder than a feral druid, for instance) but it's far more resource and GCD locked. Warriors have historically traded off those limitations (needing to build up rage, needing a nice stationary fight, needing lots of adds) for their strengths of higher armor and health and a nigh-infinite feedback loop that grows with available targets. With those gone or reduced drastically, the amount of bite a warrior's single target and non special attacks deliver needs to increase as well. Frankly, in a rage normalized world without WW or Cleave spam, Titan's Grip doesn't require that drastic damage decrease. You won't be hitting up to four targets with both weapons instantly anymore. The stats of the offhand weapon will just go to offsetting the inherent weakness of the warrior's purely physical damage in a world where Sunder only stacks to three and armor penetration is impossible to gear for.
You can see this to a degree now in how arms falls behind fury for high end raiding. Arms already suffers the undertuning effect in PvE without the benefit of TG's stats, Whirlwind's ability to instantly hit multiple mobs with two big weapons, or other means to capitalize on high rage the way fury can. Arms is actually a well designed spec at the moment with a variety of bleeds and procs, but it's a well designed spec built on top of mechanics that it can't benefit from in the same way, a victim of baseline undertuning.
Likewise, with Sunder reduced and rage normalized the possibly overpowered nature of warrior tanking (that nigh-limitless amount of rage that can be dumped into threat moves) will be gone, and when it goes, we're going to need more than Vengeance to balance it. Prot warrior DPS has been all over the place in Wrath, balanced and rebalanced to try and keep it at the sweet spot between 1/3 and 1/2 of dedicated DPS. (Right now I'd say it's close to 1/3rd... I can put out maybe 4k DPS in full tanking kit in ICC on large trash pulls while the pure DPS effortlessly pushes 12 to 15k) As a result we've been forced to rely on threat handout abilities like Tricks of the Trade and Misdirection and our own Vigilance. I don't want to see prot warriors rocket past other tanks in DPS or threat. But I do believe that warrior tanks are designed around sunder stacking and threat modifiers to the degree that without nigh infinite rage and HS spam, warrior threat is going to drop precipitously unless several other moves are increased in either threat or DPS to compensate. Rage tanks are deliberately tuned lower than mana/rune-runic pwer tanks because if they were not, then once they had sufficient rage they would skyrocket out of control for threat. With rage no longer providing that kind of benefit, that low baseline needs to come up some.
Finally there's PvP. With the hefty reduction on Mortal Strike and the loss of Bladestorm as a reliable finisher (since the second you use it you're going to lose your weapons) arms in PvP will need a significant new way to get actual damage applied to a target. There's just no way around it: without the ability to make every point of damage count double thanks to MS, arms is weak in PvP. (Note: I am not saying that arms is currently weak in PvP, but that it is overly reliant on that big undispellable 50% healing reduction, and without that, yes, arms will be weak indeed in PvP.) Arms requires a significant, potent, and reliable burst of damage to make up for what it is losing.
Frankly, I expect warriors to be very undertuned through the first few months of Cataclysm. Eventually I believe they'll be adjusted upwards to compensate for the various advantages they're losing, and I'm optimistic that the beta might actually provide enough hard information to get those fixes in sooner rather than later. With the overperforming counterbalancing abilities either removed or reduced/rebalanced, the basic undertuning will show through and will be redressed.