It impresses me to no end that Greg Egan, a talented science fiction writer [1], finds time to contribute to mathematical curiosities like this! I suppose it keeps him sharp, given that his novels often involve a lot of heavy math.
I often regret not having made more efforts to study Maths when I was younger.
I see the joy of being drawn into these fun explorations and I regret that these were not used in class to entice kids into wanting to go beyond dry textbooks that focused on theory and never tied the material being taught with anything remotely exciting.
I can't help but think that the reason some of those holes have serrated edges is due to the problems representing the actual numbers with floats. I can't say for sure, it's really just a hunch. The patterns are fascinating either way.
At least the bulk of the article was discussing data explicitly described as being generated by Mathematica, which is capable of arbitrary precision. It seems just as likely that this mode was used.
[1] http://en.wikipedia.org/wiki/Greg_Egan