In many cases, the actual disk *does* extend beyond what the `geometry'
implies; even after you discount reserved sectors.  If you make the
change you suggest, this space would become unusable.

It seems more appropriate to either:

a) stop pretending we have any idea what the geometry of a SCSI disk 
is, and just make it one large track, or

b) make the warning from disklabel(8) non-fatal.