According to the change log:

rdesktop (1.4.0)
   * Basic disk-, parallel-, printer- and serial-redirection

Perhaps the man pages haven't been updated. 


-- 
Andrew S. Zbikowski | http://andy.zibnet.us
 A password is like your underwear; Change it
 frequently, don't share it with others, and
     don't ask to borrow someone else's.