Some could. Amigas (and Macs too I believe?) would automatically pop up an icon for floppies when they were inserted, without needing to do anything else.
While those absolutely are technically "personal computers", everyone understands "PC" to mean "IBM PC or compatible". And yes, both Amigas and Macs had floppy detect. Actually, it was technically possible to do it on the PC as well, and ISTR some programs actually doing it. The solution to the training problem is pathetically obvious (as evinced by the fact that I figured it out while reading TFA which I just google'd) which is to train the system the first time the user successfully reads a floppy disk, and thus you know that there's a disk in the drive. But... Microsoft