The only thing the Drow Wizard and the Eye of Gruumsh have in common is a commander rating of 1 but you can't judge a Chaotic Evil commander by its commander rating.
The Pain of Command: Eye of Gruumsh
The difference between a commander rating of 1 and no commander rating at all is huge. The Eye of Gruumsh is too busy foaming at the mouth and slicing down his foes to give much thought to command but creatures still flock to his warband if only because they know that enemies are likely to concentrate their attacks on the Eye of Gruumsh instead of picking off the small fry!
With two melee attacks that inflict 25 damage apiece, the Eye of Gruumsh gives enemies few options other than eliminating it as quickly as possible. Thanks to its low AC and a vicious magic weapon that wounds it for 5 points every time it hits, the Eye of Gruumsh is guaranteed to take heaps of damage every time it fights. The question every opponent faces: can they kill it fast enough? Or will Gruumsh's double-axe-on-wheels put the big hurt on them before it goes down spitting?
Shut Up and Do It: Drow Wizard
In the Drow Wizard's case, a commander rating of 1 indicates three things: First, he's accustomed to command and expects underlings to follow his orders. Second, he's too preoccupied with arcane matters to have gotten very good at this battlefield command thing, unlike his cousin from Harbinger, the Drow Cleric of Lolth. Third, the Drow Wizard's followers may be willing to take his orders but they certainly don't trust him.
What the Drow Wizard wants most is protection from enemy creatures to buy the time to cast his nasty area effect spells. He's not the equal of the Elf Pyromancer from Harbinger but he can put some hurt on enemies who bunch up and aren't immune to cold. Given the Wizard's desire for protection against enemy creatures, his commander effect of increasing the damage inflicted by opportunity attacks made by his followers works splendidly for him.