The key words are "under pure gravity loading" which means if there was no wind, earthquakes or occupants. These forces are more significant the higher the buil

The key words are "under pure gravity loading" which means if there was no wind, earthquakes or occupants. These forces are more significant the higher the building. I wouldn't be surprised if including wind would halve the limit. I also think they mean something that could be practically recognised as a building. You can build much higher if you are not restricted by a traditional proportions of a building (for example a pyramid or dome). As to the building sinking -- it is not a difficult problem to solve. The reason some buildings face problem is that this is just a cost issue -- they guessed they need X amount of effort to provide stable base for the building and they guessed wrong. In practice there exists very simple algorithm to provide stable base -- drill to the rock face and use the underlying rock rather than possibly unstable ground. The reason this is not always used is because it can be very costly.