The 770 already has Bluetooth built-in, which is fine for peripherals. USB has two primary benefits: cheapness, and availability. Many things aren't available in Bluetooth.

Wireless USB is much less common than Bluetooth, and there are very few peripherals that support it. The 770 doesn't have it. So, you'd need to plug a wireless USB hub into your 770, with a battery in it, and get all new wireless USB accessories, each with batteries...