Yes, it means you are feeding those same animals 5x as along, 5x as much, 5x the food costs in their lifetime. But you are also making 5x the donation money and they are entertaining ticket-buying visitors 5x as long...so that all balances out.
That and you'd just have a new animal of the same type in the habit after they died, so the end result on your zoo is just that you have to spend less time worrying about your animal population and can spend more time just enjoying the animals.
You're actually hitting the nail on the head regarding why they implemented it this way....almost everything is tied to game speed so just slowing down game time, like some people want, impacts a ton of the game systems, not just the animals. That would require a whole lot of rebalancing if they tweak that. So they left it alone and just disconnected animal aging from the clock for those of us who don't want our animals dying before we can even finish getting their habitat looking just right.
