I suspect though I have done no checking on this that the southern ocean comes about by the fact that although Indean, Pacific and Atlantic oceans strech as a single body of water to the Antartic without major landmasses intervening this is not entirely true shouth of Australia.

That being left aside, North Athlantic, South Atlantic, North Pacific and south Pacific are often classified as seperate oceans.

As for continents, then number depends on how you define a continent, and how finely you draw these line. Some possible lines which could be drawn are along geo-political or cultural lines (this could yield far more continents), by tectonic lines in which case the boundary is a tectonic plate boundary, and yet another would be by continuous surface landmass in which case there would be fewer (as Perderderabo said: why is Europe a different from Asia or are North and South America two continents or one)

In fact even as things currently stand there are many that would argue that Indian sub-continent is in fact a full continent. If you were to draw the boundary as a major cultural change or landmass change I think you could easily get the 13 continents Perderabo mentioned with most notably Asia being further subdivided.