Oxygen is common in the crust, but the total amount of hydrogen on earth is so tiny relative to the total mass of the planet that the fact that the land to ocean surface coverage is roughly comparable seems like an incredible coincidence. A 1% deviation of the hydrogen mass ratio, one way or the other, and the earth would flip from a single very deep ocean to a completely dry desert. In this scenario, earth-like planets would be extremely rare.

On the other hand, if water is produced continuously from volcanic activity in the crust and lost continuously through UV disassociation and loss of hydrogen to space, an equilibrium might be established which would keep the planetary surface partially wet until the reservoir of H2 in the crust was exhausted. Free 02 in the atmosphere would form an ozone barrier to prevent disassociation of water to its components, but I don't see how this mechanism could feed back to the water formation process and prevent the creation of excess water. In this scenario, all earthlike planets would be flooded.

The earth, with 70% water coverage, may be a very rare planetary type. Keep in mind, if you bulldozed the continents flat and spread them out evenly in the ocean basins, the world ocean would be an average depth of close to two miles, but the Earth has a diameter of 8 thousand miles. The oceans are a very thin film of moisture on a very big ball. Either we're extremely lucky, or some mechanism operates to maintain this water level fairly constant over geologic periods of time. Perhaps this mechanism is a factor on other worlds, too.