Generally I guess. I mean, there are places where it differs, like Las Vegas has some really awesome (but tacky) rooms from what I've heard from friends who have been, and all differ.
But for a place like Paris. You'll be getting 2 single beds, a TV with satellite, internet access point and a minibar in a standard 5 star exactly the same as you would in a 4 star. Paris has that extra thing a lot of historic cities do though, and that's historical architecture offering views. So a lot of the hotels near the Arc De Triumph on the Champs Elysee are really, really expensive during peak times.
But basically, I would say the food is always the biggest divider between 5 stars and 4 stars.
That's not to say you can't eat good food at a 4 star though, and it's all dependent on the person. I mean, if you've travelled on a city break then you'd likely want to eat out rather than in the hotel and experience some more 'local' cuisine.