basic, the life of a water pump is dictated by quality pump and coolant condition. never met a water pump that lasts literally forever. they are considered a "consumable" item. just like plugs and oil.
sounds like you have a V6 toy config. reason why the pump and timing gear are linked is the cost of maintenance involved. to access water pump, timing belt needs to be removed. since both the pump and timing belt require same labor (lots $$$), if behooves one to replace both if one or the other fails. so labor intense/cost, kits for this maintenance include both.
I wouldn't want to replace timing belt just to have water pump replaced in say 1000K later. or the other way around. pay that labor again?
and BTW, toy employs AISIN foundries hard parts. best in weight class. and rockauto, amongst others, sells AISIN kits. the kits, w pump/t-belt, and pulleys/tensioner, are just a little over $200~. so it's not the parts cost that kills you, it's the labor cost involved.
but me thinks you're caught up in what lots of ppl have issues with. to not void warranties, one has to go w the dealer. and they are all very pricey. prolly looking at $120~ an hour. at that price, I wouldn't listen to them. having to go dealer, get both done. save on labor cost in long run. not doing so may allow that dealer to tag you for same labor cost just down the road. dealers employing your mentioned tactics for more revenue? eh, say it isn't so......lol.
EDIT respond to comment.
title Q is answered in my first sentence.
second Q, the manual states to inspect water pump. not replace unless required. but that brings us to your third Q.
third Q is answered in my second paragraph. explaining how the two components and maintenance schedules are linked. saving labor costs.