> What is the reason that it has been set up that way? 

Follow this thread: 
http://m0n0.ch/wall/list/?action=show_msg&actionargs[]=97&actionargs[]=22

> All other mailing-lists I attend sends replies back to the list, so
> everybody per default benefits of the discussion.

Sweeping generalities don't accomplish much in an argument.  I believe 
all sourceforge lists are configured in this way.  Someone should let 
them know they're being abnormal.

(Reply-All is your friend.....)

--Michael I.