The story that the Inklings are actually made of ink also goes with the two main gameplay mechanics: Swimming in ink and going up walls that have ink on them. Think about it, how would the Inklings swim through the ink if it's a very thin layer, rather than a pool of it, by being made out of ink! Also, why would they be able to swim up walls, because they're made of ink. Why would they pop/get slowed down by enemy ink, because they're being mixed into the enemy team's colored ink.