But what you're suggesting here, really, is that while I *could* do that, I would really need to tweak these monsters (re-design them, essentially) or else, yes, they will end up bland and flat.
I really think this is best.
Looking at the level 8 example, the average damage is 2d8+7. I tend to modify things a bit, according to the flavor of the monster.
Let's say it's an Orog soldier with a greataxe. I might be tempted to change the hit line to 2d12+3 (1d12+27 on crit) and target is marked. Then probably give them a backhanded swing, as an encounter power to have them make the attack against two targets once per encounter, and a deathblow, and give them an aura 1 that slows if you start your turn in it. This makes the damage more swingy, and very scary on crits, and holds to some of the bloodline features of orcs and ogres, as well as an ability or two that makes them soldiery.
For a drow skirmisher with a longsword and hand crossbow, I might make the crossbow and longsword hit lines do a little less damage, but give the drow a bonus for combat advantage, and add a poison to the crossbow. While they might do the same average damage, they won't feel the same. Hand crossbow hit line would be something like 2d6+4 damage, and ongoing 5 poison damage and slowed (save ends both). The long sword would do 2d8+4 damage and the drow can shift one square. The drow would also deal 1d6 additional damage with combat advantage. And of course they have their cloud of darkness to make it easier for them to gain combat advantage.
A level 8 goblin lurker with a dagger might do a measly 2d4+7 damage on a hit, but gain +1d6 with combat advantage, and another +1d6 against bloodied targets. And he maybe weakens targets on a recharge, and has shadow walk, gaining concealment when he moves 3 or more squares.
It's not the damage that makes a creature unique, it's how they deal that damage, and their other abilities. So behind the screen even if you were rolling 2d8+7 for a greataxe, a longsword, and a dagger, the players would never know. But telling them how the bonus damage is gained, gives them more options for tactics. The cleric might be inclined to use Beacon of Hope to weaken Orogs in an encounter, as well as for better healing against their brutal attacks. The wizard might be inclined to thunderwave the drow out of their darkness. The dwarf might decide he can tank the drow fairly well because of his resistance to poison. The warlock might decide to infernal moon curse the goblin lurker so he won't easily get combat advantage or concealment.
The more varied the monster tactics are, the more fun solutions PC's will have to deal with them. So for monster design, I'm typically more inclined to give monsters conditional damage or typed damage to boost the damage up to (or beyond) the average expected damage, but leave an unconditional damage value not too far below the expected average. This is especially true for soldiers, brutes, and skirmishers.