It's not just oceans. With Geospatial you can never draw a straight line between two points. Most of us work in geographically limited data so it doesn't matter much, but with larger distances the differences can add up fast. Geospatial is always dealing with the surface of the sphere(ellipsoid).

I used to have to deal with data that would be disqualified if it was more than 300m from a given point. In some cases the difference between Nautical and Standard was enough to drop a few points.

What this has to do with SQL Server vs. any other db I'm not sure.