Are you sure spa says so? They would usually have a clause stating compliance to whatever new rules and laws implmented by the government. As such these blanket statements is deemed inclusive.
And thread title need not be exclusive to just infiniti tower purchaser, purchaser of commercial products such as atria sofo, arcadia dpc, etc are all slap with the gst portion as well.

interestingly the letter from the developer to them mention revision in the SPA.
perhaps not all loose ends were covered effectively.