In Singapore, the streets are well planned and maintained, smooth and clean like everything else. However, the sidewalks have one illogical aspect: the pavement is smooth stone, which gets very slippery when wet. Singapore is tropical and humid, with frequent rain. When initially paving the sidewalks, it would be easy and probably cheaper to use rougher covering (asphalt for example) that would not get slippery in the rain. After the smooth pavement has been laid down, changing it is of course costly, and if the locals have adjusted to the slipperiness, then switching the sidewalk cover may not be worth it.
The University of Queensland has a similar problem with the sidewalk in front of its main building. The sidewalk is coarse, like yellow asphalt with 1 cm stones in it instead of sand. One would expect such a coarse surface to provide good grip in all conditions, but unfortunately the looks are deceiving. When that sidewalk gets wet, it becomes slippery like polished glass. Again, it would be cheaper and more practical to pave that sidewalk with asphalt.
A broader point generalising the above observations is that things should be field-tested in realistic conditions before putting them to widespread use. For example, the sidewalk stones should be walked and biked on under all local weather conditions before paving a street with them.
Perhaps the smooth stones in Singapore are meant to make street cleaning easier. Still, there are materials that do not become slippery when wet and are smooth enough for mechanised cleaning and cheap enough to use as pavement.