My guess is that the USB3 compatibility issue must be related to data transmission speed, but that might be more of a WAG than a SWAG. And it might be more of a software problem than a hardware problem. MIDI data is traditionally transmitted at a particular speed (or range of tolerable speeds?), so presumably that's the speed that the driver is expecting and anything else could cause the data to be garbled and unintelligible to the driver or other software. Although it's now technically possible to have faster MIDI data transmission speeds, I assume the driver needs to be able to handle those faster speeds. Anyway, that's the theory that makes sense to me, hence it's likely utter nonsense!
Regarding the installation of device drivers, you definitely need to follow the instructions given with the device. Case in point:
About a year ago I bought a used YPT-400 keyboard that seemed to be incompatible with the Yamaha USB-MIDI driver I'd already installed for my PSR-E433 and PSR-E443 keyboards-- the YPT-400 wouldn't show up as an available MIDI device, only as a USB device that (according to the computer) didn't have the correct driver installed. None of the older Yamaha USB-MIDI drivers would work on my computer due to compatibility issues with the 64-bit Windows OS, so I just gave up and resigned myself to having to use the YPT-400 with my iPad 2 (because, unlike Windows, it doesn't need a driver).
A few months ago I decided to try again. I uninstalled the current driver for my OS, then reinstalled it-- and it worked! Woohoo, now I could use my YPT-400 with my computer! Except all of a sudden my PSR-E433 and PSR-E443 would no longer work with the driver. It seems the YPT-400 identifies itself to the computer as a "Yamaha PortaTone," but the PSR-E433 and PSR-E443 both identify themselves as a "Digital Keyboard." So I uninstalled the driver again, connected my PSR-E433 and YPT-400 to the computer at the same time, then reinstalled the driver. Now all three keyboards work with the driver! When I got the YPT-400 I hadn't realized that reinstalling the driver would be necessary, since I hadn't needed to do that when I got my PSR-E443 (because the driver already knew what a "Digital Keyboard" was from when I'd installed it for my PSR-E433).