I don't think it's so much a physics/chemical difference, but more to the effect that here on Earth, the ocean is a large body of water that sits on top of the stuff the Earth is actually made of (which is a solidified crust on top of the semi-liquid rock of the mantle)
On Titan, the role of the semi-liquid rock is played by the "ocean" (and the crust is played by the solid water ice layer ontop).
On Titan, the role of the semi-liquid rock is played by the "ocean" (and the crust is played by the solid water ice layer ontop).