It's probably because There are only a few pokemon you see at the beginning of the game. weak, rock, normal-flying, bug, grass, fighting and normal. Well, Normal types are not a common gym type. And as you noticed, in sinnoh, kanto and hoenn the first gym is rock, and in johto, the first gym is flying. In Hoenn, Sinnoh, and johto, the second gym is (in that order) fighting, grass and bug. Which kind of goes with what I said: By the time you ge to the first gym, those will have been the only pokemon you will have seen. grass, flying, fighting, bug, normal, and normal-flying types. You know, the machops, makuhitas, pidgeys, starlys, spearows, caterpies, weedles, wurmples, metapods, rattatas, bidoofs, sentrets. They cant start you off with those and then have a gym leader with dragon or ice types! get what im sayin?