The original maps..showing the epicenter as a single point source..were very misleading...
They were accurate, just that the public isn't familiar with an earthquake of that magnitude and the associated displacement. Plus these figures are several days post quake, so more analysis has been conducted and a better picture is seen. I myself am quite amazed, for comparison it would be like the whole San Andreas fault rupturing. That is very large scale.
By definition, a "center" is a single point. No matter how big something is, the center is a point. It's the place where there's as much ground motion on one side as on the other, both north and south, as well as east and west. The epicenter is the point on the earth's surface which is directly above the actual center, which is the point where there's also the same amount of motion above it as below it, as well as in the other two dimensions.
Epicenters are in fact single point sources. That's where the rupture BEGAN...the fault slippage, however, propagated northwards from that point over 700 miles.