I gave Sorcerer vs. Warlock some more thought on damage.... Obviously, there are two big things we need to look at - kicker damage and powers.
(1) Kicker damage.
Warlocks' kicker damage is through their curses. They need to curse a foe as a minor action, and it always has to be the closest foe. This is kind of a limiting factor, but I don't know that warlocks are really using their minor actions for anything else.
Their kicker damage is 1d6 / 2d6 / 3d6 from Heroic to Epic tiers. This averages out to 3.5 / 7 / 10.5, with an increasing central tendency from tier to tier. The real limiting factor is that it can only be dealt 1/round.
Sorcerers get kicker damage from their secondary attributes. For sake of argument, I'll assume this will start at a 16 and get improved at every opportunity. (Naturally, some will get higher and some will be lower, but 16 is a fair assumption for a secondary stat.) They also get +2 bonuses to this each tier above Heroic.
Their kicker damage will go from 3 at the outset, to 4 at 8th level, to 6 at 11th, 7 at 14th, and 10 at 21st. This is reliable - that is, there's no chance of higher or lower.
It's about even with Warlocks, but its advantage is that sorcerers don't need to curse their foes, and can deal it to every target in a burst or blast.
Conclusion - I think Sorcerers have a slight edge here, but it's not really an excessive one, IMHO. The average kicker damage looks like it scales very, very closely between the two classes, absent any special feats or magic items. It's only in bursts and blasts that the difference becomes substantial.
(2) Powers. I'll look at the at-wills, then the most damaging dailies from (just randomly) 1st, 15th, and 25th levels.
At-Wills
IMHO, both classes are about even, with a few oddballs.
Warlock:
Eldritch Blast is the default. I'm considering this the baseline.
Dire Radiance does lower damage by an average of 2 points, but has a pretty excellent control effect. Also, it's Radiant which is a great damage type.
Eyebite does lower damage, also, but basically acts as a +5 to all defenses against the targeted creature.
Hellish Rebuke also does lower damage, but again, deals pretty sizable extra damage on the not-too-unlikely event of the Warlock suffering damage.
Sorcerer:
Acid Orb is basically Eldritch Blast that deals acid damage. Sometimes that's a plus, sometimes not.
Burning Spray is quite good - Warlocks don't get a burst power. Damage is fair, and the bonus for Dragon Magic is minor but nice.
Chaos Bolt is like Eldritch Blast, but with a small kicker for Wild Mages.
Dragonfrost is a very good power. It's a slightly less damaging Eldritch Blast with a Push 1.
Storm Walk is great for warlocks who might get into combat. It's Nimble Strike, more or less.
Frankly, when it comes to the At-Wills, I can't decide which is better. The Sorcerer does slightly more base damage, but the Warlock's control effects are simply stronger. I would personally rather have more effects for a slightly smaller die size, but YMMV.
Dailies...
Warlock 1: Flames of Phlegethos is the most damaging, with an ongoing 5 whether or not the attack lands.
Sorcerer 1: Tied between Chromatic Orb and Dazzling Ray. I think Chromatic Orb is slightly better, but more random.
I don't want to call it, but I think Sorcerer has maybe a slight edge.
Warlock 15: Lots of good ones, all of which can be sustained. Tendrils of Thuban is a good one, dealing 4d10 damage in a burst 1 and creating a Sustain Minor zone. Fireswarm also deals 4d10 damage, and with a Sustain Standard it can wreak havoc if the rest of your party kicks in to push enemies towards your target.
Sorcerer 15: 4d10 is the cap damage with Spitfire Furnace, but in a blast 3. It also gives an aura which deals fair damage to every creature next to you every round.
Honestly, I can't call these two, either. Both also have other power choices that could be excellent - for example, Curse of the Golden Mist could completely lock down a low Will target for a very long time.
25th level....
Warlock: I kinda like the 15th level ones better, but Curse of the Twin Princes is a pretty good one. It's 4d10+Cha damage, and basically lets you pass your damage off to them. Tartarean Tomb is the same damage, and can completely lock down a foe who can't save. Thirteen Baleful Stars is a quick Stun power, and everyone loves those.
Sorcerer: Words of Chaos is a lot like Curse of the Twin Princes. Slightly more damage, but it's also more random. Force Storm is great against hordes, but seems REALLY situational. Draconic Incarnation is a huge close burst, with a nice extra control effect.
So yeah... after looking pretty closely, I am just simply not seeing how Sorcerers are absolutely better... I think Warlocks more than hold their own one-on-one, and any shortfalls are fairly well-compensated by their pact boons...
-O