Guys, you seem to like complaining about some of the dragons being able to fly... They don't get flying just because the picture has wings, they have flying to balance the game better. The dragons are all supposed to be pretty much equal, so having some without flying is silly. Have you noticed that the only thing every element has in common is the fact that it has a dragon? This is because dragons are the universal "hard hitter". They aren't special, but they're there to let every element get past shields. The only shield that dragons have troubles against is the gravity shield, but gravity shields don't block the numerous small critters that every element has.
anyway, reasons for the gravity, earth and aether dragons attacking:
The aether dragon travels through another dimension to reach you, or he teleports or something mysterious/magical like that.
The gravity dragon uses his excessive weight to create a gravitational pull strong enough to pull you towards it so it can hit you
The earth dragon...throws large rocks at you?