yes, that's a fair point. it is entirely at the discretion of the government.

that being said, if it weren't, the concept of a 99-year lease wouldn't have any teeth.

indeed, your point is a central pillar of the land development policy in singapore -- the idea that things evolve and the government needs to make decisions for the 'greater good'. the same concept exists in the usa (imminent domain; a completely different implementation but still one that strips assumptive rights that a property owner has).