Eh... Most steerer tubes are aluminum for exactly the reason that you've shortened a lot of forks. In the field, Joe Mechanic is less likely to screw up an aluminum steerer vs. a carbon one.
As to what's rare, hell if I know. Aluminum forks are fairly common on low to mid-tier bikes and the cheap ones tend to suck.
As to what's rare, hell if I know. Aluminum forks are fairly common on low to mid-tier bikes and the cheap ones tend to suck.