For a time, windows would more readily run an autorun from a disc than from a usb stick. Even if that disc was in an emulated usb disk drive.
That's because there was malware that spread via autorun, which is rather harder to do with read-only media, even if it's emulated.
And the "u3" flash drives that did this were a hot commodity for a little while!
Then came the iODD and the IsoStick...