Bring the player, not the class. This was the overall direction they wanted to take World of Warcraft (at least in PvE) with Wrath of the Lich King. While all classes are different and that's what makes the game interesting, the motto, "Bring the player, not the class", was all too successful and the consequences are quickly evident. It's made hybrid classes "the thing to be" and left many pure classes (rogues, mages, hunters, warlocks) with the short end of the stick.

Hybrid History

The "Triple Threat" hybrids, Druids and Paladins, are the most extreme cases because of their ability to Tank, Heal, and DPS. At level 60, these classes were mediocore at all of these 3 roles, were brought to the raid for their buffs, and 99% of the time... healed. After Burning Crusade was released, druid tanks quickly became accepted by raiding guilds due to their obscene armor/health advantage over warriors. Soon after, Retribution Paladins started to shine with their ability to keep Judgements up on the assist 100% of the time, give the raid 3% critical strike, and 2% raid damage from Sanctity Aura. With so much synergy, not much personal DPS is necessary to make the hybrid worth bringing as a DPS. At the conclusion of The Burning Crusade, guilds even started to realize the utility that Protection Paladins offered as AOE-threat tanks in Hyjal and Sunwell Plateau. By the time Wrath of the Lich King was released, it became obvious that all specs of all classes could excel in a raid setting.

Wrath of the Lich King

Druids and Paladins are able to pick up gear for all specs, have the ability to swap between two different specs with ease and no cost (Dual Talent Specialization), and fill any role they wish in any size raid. Why make an alt, when you can see the game from so many different play styles and points of view with just one character? The PvP scene has even accepted the Protection specs of Paladins and Warriors, an idea that was laughable a year ago.

The days of "lolret" and "learn your role" are over. You can either play a pure class and spam the same few buttons every encounter, or you can drastically increase the replay value of your character by playing a hybrid. Hybrids can bypass the tedious leveling process should they decide to experience a drastic role-change. The wider perspective that they acquire lets them play any role better because they've experienced things from all points of view.

And this is not going to change. Blizzard isn't going to give rogues the ability to heal or tank. The overall strengths and capabilities of hybrids are going to stay as they are or get better. If you aren't already playing a hybrid or at least a class with two different roles, consider cutting your losses and reroll a hybrid.