Anecdote: I always keep my grapes on the vine unrinsed and they last more than a week.
What do you mean you don't buy grapes and then just eat all of them in one go? Interesting tip though, I know a fair bit about plants and gardening, yet this idea never occurred to me.
IME the rot setting in from broken skin wins over the effects of vine consuming the nutrients.
Pro tip: you can grow your own grapes just by sticking a cutting in the ground. Super easy.
The grapes I buy stay good for more than a week in the fridge without doing anything to them.
Pro tip: Buy your grapes, take them home, rinse them and promptly remove them from the vine. They will last up to a week in the fridge if the plant they grew on isn't desperately trying to stay alive longer with zero hope of survival by feeding on the grapes.