alt Hacker NewsAs soon as the motors used to spin drives were able to provide a once per rotation signal to replace the index hole, the hole was no longer used for anything. The detector and lamp used to detect the hole were more expensive than using a signal from the motor.
Motor rotation isn't quite enough, as it's not aligned to the sectors on the disk.
Drives which do skip indexing (Like Apple's Disk II) use the actual data on the disk for indexing. Each sector header has a track/sector/head ID, allowing the controller to know where it is on the disk without the need for indexing.
TBH, I'm not sure PC floppies even use the index pulse for anything other than formatting the disk. Once the disk is formatted, it's kind of redundant information. But it's required by the spec, forcing PC floppy drives to include the sensor.