Webmin from 2.2 CD-Install Failure

[Carl Brown]

Attempted installation from the Tasty Morsels CD via commandline failed as 
follows:

# rpm -ivh /mnt/cdrom/YellowDog/ppc/webmin-0.92-1a.noarch.rpm
Preparing...                ########################################### [100%]
Unabled to identify operating system
error: execution of %pre scriptlet from webmin-0.92-1a failed, exit status 2
error:   install: %pre scriptlet failed (2), skipping webmin-0.92-1a

Why does a "noarch" rpm care what the OS is, and why is it "unabled" to 
identify it?