Due to the immense increase in Usenet spam (in turn due in no small part  
to Google's relative lack of interest in dealing with their contribution  
to the problem as a friendly portal for the spammers), many news readers  
do in fact include spam filters now.

But beyond that, many ISPs filter spam at the news server level.  I don't  
use my news reader's spam filter, but most of the spam gets blocked by my  
ISP on my behalf (well, actually my ISP's contracted news provider, but  
whatever :) ).

It's just a bad idea to reply to spam anyway, and it's definitely a bad  
idea to quote spam if one does reply to it.  All one accomplishes in doing  
so is helping the spammer.

Pete