I think the sidewalks caught my attention so dramatically because my views on ornamentation in architecture and public space generally have been changing. I used to be a "form follows function" kind of guy: I appreciated the clean lines of modern design and scorned elaborate designs that didn't seem to really do anything. If it isn't "doing" anything, then why waste time, effort and money building it?
Then I came across the writings of the architect Christopher Alexander. Alexander has developed a healthy dislike for modern architecture and believes that it is possible to come up with a "pattern language" that is universal and can help us design and build structures that improve our quality of life on multiple levels.
Alexander has in recent years published his "Nature of Order" series of books, which argue for the place of ornamentation in our architecture and other aspects of human creativity. I have come to agree and urge you to check out his writings, especially: The Timeless Way of Building and the Nature of Order series.
These sidewalks not only reflect a wonderful aesthetic, but also a very smart practicality. In Chicago and many/most US cities, the sidewalks are slabs of concrete. Very dull and in many ways not all that functional. With the extreme temperatures of Chicago, the concrete usually cracks shortly after it is laid in place. And in the many tree-shaded sidestreets of Chicago's numerous neighborhoods, roots cause the most delightful disruptions in the straight surfaces of the sidewalks.
Prague has similar problems with tree roots and wide fluctuations in temperature. Their "mosaic" sidewalks offer something of a solution. As temperature changes cause movement in the ground, the individual cubes will shift and sometimes pop out, but they are easily repaired, since the damage is much more localized.