off-topic ports 1720 and 6000-6009 shown even though they should be filtered

[Phill]

I know this isn't RHEL support, but I thought I'd ask this question anyways, see if you gurus know what might be going on. I have a rhel 5 web/ftp server. I'm using iptables to filter all ports except 21 and 80. Yet if I do an nmap of the server, this is the output I get.
-------------------------------
PORT     STATE  SERVICE
21/tcp   open   ftp
80/tcp   open   http
1720/tcp open   H.323/Q.931
6000/tcp closed X11
6001/tcp closed X11:1
6002/tcp closed X11:2
6003/tcp closed X11:3
6004/tcp closed X11:4
6005/tcp closed X11:5
6006/tcp closed X11:6
6007/tcp closed X11:7
6008/tcp closed X11:8
6009/tcp closed X11:9
6017/tcp closed xmail-ctrl
6050/tcp closed arcserve
---------------------------------

Note the listening port 1720, netstat shows no service listening 
Should be irrelevant since the only traffic I'm accepting is  port 21 and port 80, and related established. Shouldn't this output just show me port 21 and port 80 open and nothing else?