We think a cornerstone of good gameplay is making interesting decisions.Well, it is official now: Blizzard agrees with me that gameplay in World of Warcraft should not exclusively be based on execution, but that making interesting decisions is a cornerstone of good gameplay.
Ghostcrawler was responding to players complaining that making healing more challenging in Cataclysm was sign that "Blizzard hates healers" and "nerfed" them. It is easy to see why that accusation is impossible, even theoretically: Healers are not in competition with tanks or damage dealers, thus any changes that affect *all* healers are strictly neutral. If anything, healers are better off when healing isn't too easy; not just, like Ghostcrawler says, because "easy healing" means mindlessly pressing the same button over and over, but also because the easier healing gets, the less slots does a raid need to reserve for healers. Imagine the ultimate healing spell, which for 1 mana heals 1 million health for the whole raid as an instant: Every raid, even 25 man, would just need to take a single healer with them, and he'd just be spamming that one button. I'm much in favor of the Cataclysm solution of making healing more challenging, and much more interesting to play.
So when comparing how much Blizzard "loves" or "hates" the three archetypes, we need to check how much these archetypes are in demand in a raid or group situation, and how well each archetype performs outside of groups in soloing. Obviously damage dealers come out on top in this consideration: A raid will always try to take the minimum number possible of tanks and healers, and give all the remaining slots to damage dealers. Damage dealers have a reserved 60% of slots in 5-man groups, same or better percentage of slots in raids, and solo play is designed in a way that maximum damage advances you fastest. As in groups there are always several damage dealers sharing responsability for the damage output, a dps player can more easily get away with underperforming than a healer or tank. Damage dealers only have two problems: As it is so blindingly obvious that they are so much better off than tanks and healers, far more than 60% of players go for this archetype. And playing a dps involves a priority list or spell rotation which is independant of what you are actually fighting, and thus playing a dps often lacks those "interesting decisions". That has social consequences as well: Playing a damage dealer is considered easy mode, suited for those who can't cut it in the more demanding roles, and that attitude is reflected in pejorative terms like "huntard" being thrown around, regardless of how intelligent a particular player actually is.
Healers are pretty much in a sweet spot right now. Because less people want to play a healer than are necessary for a group or raid, healers can easily get spots in groups and raids, and have only minimal waiting time in the Dungeon Finder queue. The demand for healers goes up when moving from 5-man groups to raids. And dual spec allows most healers (sorry, paladins) to switch into a caster dps spec in which they can perform very well without having to switch out of their healing gear.
If Blizzard "hates" any archetype, it must be tanks. While tanks get into 5-man groups and 10-man raids as easy as healers, there is only one "main tank" in every raid, even among 25 players, and the other tanks are just necessary for bosses with abilitities that necessitate a switch, or for "off-tanking", and 25-man raids usually need less than 5 tanks. Tanking gear, even after the removal of the defense stat, still needs lots of stats which are basically useless in solo play. So tanks are either condemned to be less efficient than others in solo play, or they have to collect a second set of gear to switch roles to dps.
So if Blizzard wanted to further improve class or role balance, they would need to make damage dealing involve more interesting decisions, for example with a system of changing resistances and vulnerabilities of mobs forcing damage dealers to switch from one type of damage to another. They also would need to make damage mitigation or healing more important in solo play, so tanks and healers would do better in solo mode. But those are theoretical considerations, and Cataclysm is already an improvement over previous incarnations of World of Warcraft regarding role balance.