Since these worlds are all in the same state, they were originally named by which Internet backbone they are on, which can make quite a big difference too.
However since then RuneScape has grown quite a bit, and we now have worlds all over the US! So it seems more sensible to just name all the worlds by their location, especially since lots of players have been asking why we don't have worlds in California.
Nothing has actually changed :) The performance and the way these worlds work is exactly the same as before. They are just named differently.
Thanks
Andrew