This goes for any role -- AoE damage, healing, what have you -- as we go forward. When the stated goal is to encourage single-target DPS on pulls that aren't specifically "many whelps"-style trash swarms, asking for more big AoE damage doesn't make sense; they're trying to encourage the use of single-target spells, they've said so, the last thing they're going to do is give you "Firesleet Conflagration" that hits everything for tons of fire and frost damage. If they want to encourage healers to watch their mana bars and use a variety of healing spells, not just their biggest spells, they're hardly going to give them a huge, mana-friendly bomb of a healing spell that they can just spam all day.
The difficulty for us as players here is that we have only our previous experience of the game (sometimes up to five or more years of said experience) to guide us. The developers can tell us, "Well, you won't be using that as much in Cataclysm," all that they like. It's hard for us to look back at the history of the game and believe them, especially when we've been given few specifics to take apart yet. For myself, I remember when I had to stance dance to battle in order to throw a Thunder Clap off to slow a boss' melee swings, or hit three or four mobs at most to try and get them to stay on me when tabbing furiously and hitting Sunder (before Devastate even existed yet) to try and build some AoE threat. The beginning of Burning Crusade and the horribly broken way they implemented rage normalization has never left me. Three years later, it still stands out as having been so bad that I nearly quit the game altogether. It's very tempting to assume that the new rage normalization coming in Cataclysm will be just as bad.
It's a tendency that is understandable and to some degree impossible to fully stop, but we have to keep it under control. We don't know what the new healing mechanics will play out like, we don't know how DPS rotations will look, we don't know how pulls will play out in the new dungeons. We don't know if we'll be happy with the way rage works, we don't know if blood as the only DK tanking spec will be a blessing or a curse. As players, we have to resist clamoring for solutions to situations that we've come upon in the past and prepare for problems we don't even know we'll have yet.
Insisting for solutions that make a style of play we're not even going to have in the future won't get us anywhere. We have to prepare for the expansion at hand, not the one we just had. It may turn out that we'll have all the AoE threat we could possibly need but need a short-term cooldown to deal with increased damage from harder-hitting single mobs. We might need a spell that helps deal with burning too much mana while healing both a single target who is taking big amounts of damage and also a raid that is taking reliable amounts of small damage. We might need spells that help bridge the gap between single-target and AoE situations for fights where many adds spawn and its too much of a mana drain to switch tactics. We don't yet know. But asking for abilities to let us do what we know we're being encouraged not to do is completely counterproductive and nonsensical. Now is the time to look forward.