It shouldn't apply to voidspawn because:
- zzrot portal isnt available at the start of the game. You need 2700 gold to buy the item, and when it is bought it is situational and only one player out of ten on average will have it.
- voidspawn move down lanes, meaning they always come out of fog of war when they come into contact with enemy minions. The clarity with is no different from an ally minion coming into contact with enemy minions.
- voidspawn pathing is predictable and they trace a path to the void portal they came from. That is a more of an accomplishment to kill one of those. If it doesnt give gold already it should, but even if it doesnt then the zzrot owner has to wait to place another one, and so the enemy has createdan opening to do other things.
Also, I would say that if you had to defend a tower for two minutes against this item, then you didnt deal with the threat early enough. Voidspawn are easily killed by tower shots and need minions, so the wave and voidspawn would have had to built up for a while before the situation you described happens.