Yes. And the chance to kill in one hit, vs the chance to miss entirely, is what balanced them against each other. Unless you can pinpoint for certain that an enemy has 7 or less hp - which is hard to do, and a relatively rare occurence - than the At-Wills are about equal. MM is an acceptable choice, sure - just not the only choice.
Several people keep claiming that a) pinpointing that the foe has 7 or fewer hit points is hard to do and b) the enemy rarely has 7 or fewer hit points.
Are these true?
At first level, non-Strikers tend to do about 7 to 10 points of damage on a successful hit.
Strikers tend to do 15 to 20.
Standard first level foes have about 28 hit points (some a little more, some less).
Is it really that hard to know that if a Striker and a non-Striker has hit a given foe, that one more good hit will probably do him in at first level?
Yeah, he might once in a while have 8 hit points at that point in time because he is higher level or the PCs rolled low damage, and MM takes him down to 1. But, he's not typically going to have 15 hit points remaining.
Standard second level foe? 35 hit points. Standard third level foe? 43 hit points.
This is not rocket science stuff here. Yes, the player will not typically know what level the foe is or necessarily if he is standard or elite, but then again, most encounters have multiple foes of the same type. It doesn't take much to realize that if the group has done ~50 hit points of damage to dead foe #1, and ~40 hit points to merely bloodied foe #2, that foe #2 is on his last legs.
As to how often a foe will be in the 1 to 7 range, that's more common at low level than people seem to think.
Every NPC that dies has some number of hit points before he is killed. And, the NPC tends to get bloodied first before this happens (unless he gets killed outright by a Striker while still not bloodied).
So, a first level standard NPC has 1 to 14 points remaining when first bloodied. From a probability standpoint, that means that your average first level bloodied foe is probably in the 1 to 7 range about half of the time before he dies.
A second level standard NPC has 1 to 18 points remaining when first bloodied. From a probability standpoint, that means that your average second level bloodied foe is probably in the 1 to 7 range about 40% of the time before he dies.
A third level standard NPC has 1 to 21 points remaining when first bloodied. From a probability standpoint, that means that your average second level bloodied foe is probably in the 1 to 8 (Wizard has +1 implement by then) range is still about 40% of the time before he dies.
So, an easy rule of thumb is: If a foe is bloodied at low level and one of my allies has hit but not killed him after he got bloodied, there's a fairly high chance that a magic missile will finish him off. If a foe is hit hard three times by non-strikers, or hit hard once by a striker and also hit by a non-striker, he's probably in or close to single digits.
Without keeping track of how much damage a foe has taken, how much damage other similar foes in the same encounter took before being bloodied or dying, these simple rules of thumb could allow a Wizard player good odds on picking off single digit NPCs.
Like counting cards at a casino, how much does the Wizard player's odds increase if he does pay attention to how often foes are hit and how hard to some minimal level. And as levels go up (with ~7 or 8 or so combat encounters per level, depending on how many skill challenges and how tough encounters are), wouldn't the Wizard player get better at guestimating when it's a good time to use MM and when it is not?
I'm thinking that the claims that this is hard to do and infrequent have no real data to back them up. I know that my in game experience allowed me to do it frequently. Not that I choose to do so every time, I almost always choose to do an area effect if I could (sometimes even knowing that one guy in the area was on the cusp).