Not all classes are even (in most games). While the player base may feel that developers have favorites, the people behind the game often do enough to deny such claims.
However, Blizzard's latest revelations about the Rogue only legendary leaves little to the imagination. Previously, legendaries seemed aimed at certain classes more than others, but not to this extreme. Let's review the weapon legendaries to date:
The first legendary was, in all honesty, a bit bland, but nearly any class could use it since it was based on weapon skills, not classes. It was pretty good, but famous mostly for its looks. For this reason, warriors, shaman, paladins, and even druids wanted it (though guilds that gave it to a druid were usually mocked), and while warriors usually made the best use of it, guilds could reward this to a wide range of worthy people.
Next, the trade chat spammer came. Aside from becoming terribly over-linked over the years, Thunderfury was, again, useable by several classes, though due to the generated threat, often given to tanks. Still, I remember seeing rogues and even a hunter with this item. I'm sure there are shaman out there who have it as well. Simply put, it was still flexible in terms of who could make use of it, since the sword proved popular with pvpers.
Then came Atiesh. A rather flexible legendary, Atiesh was the first caster legendary, but far from the last. The nice thing about this legendary (other than being an ulta-status symbol since Naxxramas was not accessible to most of the player-base and because the quest-line was taken out of the game before the launch of the third expansion) was that it had several forms. Again, Blizzard gave it some wiggle room so that no one class could claim it as their own. This was also the first legendary with an on-use effect, summoning a portal to the first raid of the upcoming expanion at the time.
After that came Burning Crusade's Warglaives. At the time, only 2 classes could use these- the first time a legendary had been given to such a small potential audience. However, it wasn't a huge issue, since 25 man raids were king, and I had personally never heard of a group not having any warriors or rogues.
Following this came the rather restrictive Thori'dal bow. Without a doubt, this bow was made for hunters, since hunters were (and still are) the only physical ranged class in the game. It also replaced a nearly-required item used by many hunters (the ammo pouch, since back then, you did not have unlimited ammo unless you had this bow). Still, I saw a warrior and a few rogues with it as well, since there was no class restriction on the item and was still pretty good (even for rogues who made macros to switch to a thrown weapon for deadly-throw). The infinite ammo still helped warriors and rogue since it saved them some back space, so none of the mechanics only helped hunters.
Then we got the healer hammer. Yes, some casters also wanted it since it gave them some good dps, but only healers could get it to proc. Since there were 4 classes that could make use of this legendary, it wasn't much of an issue for the most part, returning us to the Vanilla WoW days of flexible legendaries (I think a rogue or warrior could even euqip it if they got enough help making one).
I don't think many people were too surprised by the final Lich King legendary besides the fact that it had class restrictions on it. Hunters, for example, can use 2 handed axes, but Blizzard decided to make this for melee DPS only. Still, 3 classes could use it, and none could really argue that they deserved it much more than another, unlike Thori'dal.
Cata's first legendary, Dragonwrath, lacks class restrictions, but it more suitable for caster dps. Like the healer hammer, it can potentially be used by those who wouldn't get the most out of it (like a holy priest), but it still gives the ability to a wide range of classes. which is good, because this is also the first legendary to grant a buff to the user (in this case, turning them into a mount).
Now, getting back to the rogue legendary, we run into a few issues. The biggest problem is that, unlike any legendary previously available, the daggers grant a class specific abilities. DPS or healing procs are one thing, since several classes can take advantage of them, but "finishers" are a mechanic unique to rogues. The quest line also sounds like it will involve rogue-only mechanics, hinted at by the use of "stealth." Legendaries often have quests associated with them, but Blizzard's wording makes it sound more like a class-specific quest. Finally, keep in mind that WoW's raids have shrunk tremendously, and with classes looking more similar, there are many 10-man raid groups who do not have an active rogue to give this to.
Now, some careful readers may argue that finishers and stealth are skills held by druids as well, but they are unable to dual wield. If pick-pocketing or disabling traps are involved (I'd assume that little part about being "clever" is indicating these), the quest itself will prevent druids from benefitting from the daggers even if the main hand grants the abilities and scales for druids.
Some of this is speculative, but as things stand, it seems like Blizzard's showing an awful amount of favoritism towards rogues. It's very hard to argue the flexibility of an item that grants class specific mechanics and constantly uses the classes' name in describing said item. Previous items/quests from raids that favored a class were removed in Cata, so I'm confused as to how and why Blizzard is going down this path.