I have 3 usb drives sitting on my desk right now. The last time I used any of them was when someone gave me one, a really nice 16gb Sandisk aluminum keychain drive, with a few files on it - that was last August. I actually like holding it, because it's small and feels good in-hand, but I'm not using it for anything, nor the other 2 drives, a 32gb and 64gb I bought a couple of years ago to increase the capacity of my '11 13" 128gb MB Air (before I replaced the internal drive with a 256gb strip).
Sure, I'll agree that Apple could have included adapters, but they're not about providing solutions to keep people using things from the past, even if the consumer kicks and screams about it. Times are changing now, not just in the future. The reason usb drives are so cheap is because they're at the end of their life, in the same way that CD-rom's went from $5 each to packs of 20 for $5 (or less) or how the floppy disks before cd's did the same thing.
when was the last time you put a CD into a PC? The elimination of USB drives Is going to take a bit longer than how quickly CDs became obsolete. But with basically unlimited cloud storage and pretty fast wifi for all, I think the majority of folks will not be using USB drives in three years.