I can't say I've seen wall plug sockets with USB ports in them before.
But I have a few extension leads which have their own USB ports.
I don't see any point of these, unless it provides any sort of connectivity.
Every USB charger I've ever had has an adapter to plug in to a standard outlet, doing this you're just losing regular outlet slots.
I'd agree with that when it's a wall socket, but if it's an extension lead then it's very useful even without connectivity.
Being able to plug in a phone charger directly into a USB port on the lead means that you save an entire plug socket for any other object you have which needs a plug.