Indeed, there are other technologies that can build a digital clock more easily, but I think the point was to further demonstrate the versatility of CSS. I've personally never before seen CSS do something like this. I also enjoyed how the author took the time to explain how div borders were used to create the numbers.
If that was new to you, then this should blow your mind (it certainly did mine 3 or 4 years ago). It uses roughly the same border trick to draw a 3d rotating polygon.
