conjecture: without plate tectonics and a hot, soft mantle (aesthenosphere)/liquid upper core, there would be no oceans. solid rocks can absorb water (crystalline structure is somewhat porous) as well as chemically bind water (see this), but magma/heated rocks drives water out (and to planetary surfaces). one potential reaction is the transformation of olivine to serpentine and back. the oceans may be deep; the lithosphere is even deeper.
one implication: martian oceans drained beneath the crust and became chemically bound.