I believe this is not a feature but a limitation...

Theoretically (I won't claim whether it's a feature or a limitation), this should provide complete freedom in building (ideally, without dependencies between buildings). It also allows for balancing the construction at any moment.
As I understand it, each building has its own number of Town Points.
So, if the developers decide that dragons can only be built when all buildings are constructed in the city, they can set a requirement for the Town Points = sum(Town Points of all possible buildings), and that's it. And no direct dependencies, only indirect ones. And the balance can be adjusted with patches.