Except the flavor text of "Hammer of Gond" suggests the thrown hammer returns, while the crunch omits that feature.
It could just be referring to the fact that magical thrown weapons return in 4e. No real need to put in an extra rule.
Except Hammer of Gond isn't the name of a magic weapon --- it's a feat granting proficiency with warhammer, and the ability to use same as a thrown weapon.
Nice feat. I like having a smart guy / leader type who occasionally solves a problem by throwing a hammer at it.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.