World of Warcraft has four classes that can heal and four classes that can tank. Two of the tanking classes are classes that can only tank or DPS, and two of the healing classes are classes that can only heal or DPS, leaving two classes as jacks of all trades who can heal, tank or DPS. In general, of WoW's 10 classes, we have therefore six or so classes that can perform at least two, if not three, roles. This leaves four classes with three talent trees each which only perform one role, that being DPS.
Should this be the case? Or should the remaining four 'pure' DPS classes... the Rogue, Mage, Warlock, and Hunter... be given the same 'hybrid' flexibility as the other six? We've seen great changes from the old days especially with the release of Wrath of the Lich King bringing real viability for hybrid classes to fulfill whatever role they spec and gear for, especially with tanking and healing: each tanking class can perform the MT role, for instance, although each can be said to have strengths and weaknesses to some degree in certain aspects (Warriors and Druids struggle with AoE tanking compared to Paladins and DK's, for instance). Some healing classes excel at group healing, others at tank healing, but all should be more than capable of solo healing a five man and all are valuable in raids.