Yeah, that's not typical and the reason is pretty much practical. If you center at or near the Greenwich Meridien, the edges of your map are more or less right between Alaska and Russia and go down the middle of the Pacific Ocean where there's very little land. Of course, one 2D map projection can't cover the whole earth effectively but centering a typical projection on 0/0 gives you something that works for most of the areas people are looking for on a world map.