In a vacuum, yes, but I think someone else made the point that you need to enforce your rights vigorously to protect against the erosion of your intellectual property. An imperfect analogy: The Coca-Cola Company sends "spies" to restaurants that serve Pepsi and has the spies or order "a Coke." If the restaurant serves Pepsi without clarifying that they serve Pepsi, not Coke, then it gets a nasty letter. The idea is that Coke doesn't want its trademark to lose its meaning and become synonymous with all cola drinks.
In short, yes, this is a small fish, but I don't fault Iron Maiden for protecting its brand. More than almost any other recording artist, Iron Maiden derives a significant portion of its income from merchandise. If Iron Maiden ever wanted to publish a comic book about the band, Eddie, or anything else, it needs to protect its rights in that area. Iron Maiden may not be in the comic book business yet, but it is in the book business.
That said, they should have let Persepolis use Wrathchild -- didn't McGoohan let them use the Prisoner dialogue for free (or close to it)?