I would like to be able to disable icons for devices/mount points
appearing on the 
desktop.

Possible reasons for this behavior:
- incorrect icons are being shown
- 
user has several devices and it takes up too much desk space
- user has several other icons 
and has no space for the devices
- system administrator wishes to discourage users 
un/mounting devices
  (but still allow it via the text console)
- mount points are remote 
and it's too costly to monitor them
- users migrating from other environments do not expect 
device icons on
  the desktop

I'm not sure if any of these reasons is good 
justification.  I'll let you
decide. :-)

Apologies if such an option already exists: I 
could not find any menu
option or configuration file to disable this behavior in my 
current
version of Nautilus.