I'll elaborate a bit more. Blizzard manages damage in this game in 2 categories, melee/hunters and casters, with a bunch of subcategories. This is not some insider secret, it can simply be figured out by looking at how classes work.
Melee classes either have resources to manage (Rage, Energy/Combo Points, RP, etc.) or cooldowns (Ret paladins, enhance shamans) with some classes overlapping a bit, such as Ret managing both a resource (holy power) and CD's. This system is to prevent the spamming of abilities, since that would make a lot of classes overly complicated and impossible to balance. With this system comes another problem though, which is the amount of burst classes can put out. If you simply have all of your damage distribution from special attacks, they would hit for insane amounts, on top of being instant, while you would put out 0 damage in between. This is where auto attacks come in. Auto attacks allow Blizz to shift damage from special abilities towards something a lot more constant, auto swings. The entirety of this system is meant to give melee classes outgoing damage in between special attacks, while controlling burst and putting in resource/CD management styles of gameplay.
Casters work a bit differently. Casters do not have the same kind of resource/CD based damage system, but use mana instead. One reason for this is mana not working the same way something like energy works, in both terms of regen and sustainability. A rage or energy bar is very bouncy, depleting quicky and filling up quickly, while a mana bar slowly depletes. Casters do use CD's, Conflag in this case, but they are typically 10+ seconds and aren't the bulk of our damage. Because of the way mana works, we can't have abilities that hit hard, have a short CD AND are instant. The important part of this is the instant part, which is where fillers for casters come in. Spells with a cast time, that do moderate damage, and do not have a CD. They are meant to keep caster gameplay fluid, and for the most part keeping them stationary while using their big moves. It is important to note that casters, with the exception of hunters, are the only classes that have actual filler spells which do not have a CD. This system works largely to the same effect as the melee system in that is is meant to provide constant damage while controlling burst.
Just so I don't become too convoluted, it boils down to a few things.
Casters are stationary while melee are mobile. Casters have cast times while melee have instants. Casters have mana while melee have resources like energy and CDs. Melee get auto attacks to keep their burst low and provide sustained damage. Casters have filler spells to keep their burst low and provide sustained damage. Hunters work a bit differently because their resource can be replenished through casting their filler and because their resource depletes much faster than mana. They can also not be interrupted and with the introduction of focus had to be able to cast on the move (Aspect of the Fox).
If they give Warlocks auto attack, it is not because it's cool, it's because they feel that we need to have it for balancing our damage. If a caster is not GCD locked, yet can still maximize his damage, that means we work similar to rogues, with a fast depleting and fast recharging mana bar. It implicates that we will be burst machines, quickly using our resources, then waiting for them to recharge. We will need an auto attack at this point because we can't always cast, even if we wish to do so, since we will have to pool energy (let's scrap using mana since it won't work like mana anymore).
This brings up even more issues, suddenly we work like melee, with an energy like resource that we cannot cause to regen any faster, but we still have cast times. Now we're stationary like casters, can be interrupted like casters, but we lost our ability to chain spells. We will be sitting there, auto wanding away while waiting for our resource to recharge. We still can't cast while moving (without a HUGE drawback) so if we have to move we will suddenly energy cap, which is bad. In PvP we will be interruptable so we will always be sitting at max energy, not being able to use it because we still have cast times. Since our abilities will scale similar to melee abilities due to auto wand, we will be useless in PvP. We hit as hard as a rogue, but we're always energy capped, and can be interrupted when we try to cast. Even when we get a cast off, we can't chain cast because of interrupts, so we have the damage potential but we will NEVER be able to utilize it.
On the other hand, if our mana bar doesn't deplete very fast, we will be GCD locked, casting our main filler spell as usual, until we have the resources for a soul fire. Which we will never get off in PvP, and which will feel WORSE than early cata 2.5 second Soul Fires, because the cast time has to be long enough for a single soul fire to regen half of our mana bar (2 soulfires regen our entire mana bar, remember).
I guess one of my biggest problems with what we have been given is how little the person that gave us the info seems to know about how this game works. All of these things are quite obvious if you take 5 minutes to think about it, which I would hope Blizzard did. You cannot have a caster that is not GCD locked and is maximizing his damage while not casting, unless our resource works like energy.
---------- Post added 2012-02-23 at 05:31 PM ----------
Read my last post for why an uncapped high resource management model for a caster like Warlocks is a terrible idea.