I know everyones sick of this. But one of the gyms is a Rock type. Remember someone saying In G/S that all regions had a Rock type gym. Jasmine use to be Rock gym leader.
Although I wish it wouldn't be the first gym.
I don't mind the first gym being Rock actually. Its super-easy to beat =D Plus you get pretty decent TMs from them typically (Rock Tomb is good early-game and Stealth Rock is Stealth Rock, nuff said).