No, really. Aquaman and Spongebob Squarepants have that in common. Arthur Curry's superpowers are mainly based in him living under the sea, gifting him with a water adapted physiology which apparently means he has super strength, endurance, agility, reflexes, hearing, and senses. Plus he can talk to fish! So the sea is kind of his turf. That's where he flourishes. But not a whole lot of crime and such and such occurs beneath the waves, which means he frequently has to pop up onto land for a bit. Also the Justice League put their base on the Moon, which seems like a pretty clear message about where they want to hang out (ie nowhere wet). Unfortunately for Aquaman, spending too much time on dry land starts to render him weak. Yep, he dries out, essentially. Believe it or not it's an issue that didn't get ironed out until relatively recently, when Batman came up with a wetsuit to keep him permanently moist.
Tom Baker is the Comics Editor at WhatCulture! He's heard all the Doctor Who jokes, but not many about Randall and Hopkirk. He also blogs at http://communibearsilostate.wordpress.com/