Security – Why does nmap report different results from localhost

When I execute "nmap -sT -O localhost" per the Centos 5 deployment guide, I get:

Not shown: 1677 closed ports
PORT     STATE SERVICE
22/tcp   open  ssh
80/tcp   open  http
8080/tcp open  http-proxy

which makes sense. But when I execute "sudo nmap -sT -O -Pn my.ip.address" from another machine, I get:

Not shown: 917 filtered ports
PORT      STATE  SERVICE
7/tcp     open   echo
21/tcp    open   ftp
22/tcp    open   ssh
70/tcp    open   gopher
83/tcp    open   mit-ml-dev
139/tcp   closed netbios-ssn
306/tcp   open   unknown
366/tcp   open   odmr
445/tcp   closed microsoft-ds
465/tcp   open   smtps
513/tcp   open   login
541/tcp   open   uucp-rlogin
554/tcp   open   rtsp
700/tcp   open   epp
705/tcp   open   agentx
901/tcp   open   samba-swat
992/tcp   open   telnets
1002/tcp  open   windows-icfw
1010/tcp  open   surf
1027/tcp  open   IIS
1059/tcp  open   nimreg
1094/tcp  open   rootd
1108/tcp  open   ratio-adp
1113/tcp  open   ltp-deepspace
1151/tcp  open   unizensus
1152/tcp  open   winpoplanmess
1443/tcp  open   ies-lm
1455/tcp  open   esl-lm
1494/tcp  open   citrix-ica
1717/tcp  open   fj-hdnet
1783/tcp  open   unknown
2323/tcp  open   3d-nfsd
2394/tcp  open   ms-olap2
2492/tcp  open   groove
2557/tcp  open   nicetec-mgmt
2604/tcp  open   ospfd
2701/tcp  open   sms-rcinfo
3128/tcp  open   squid-http
3260/tcp  open   iscsi
3283/tcp  open   netassistant
3390/tcp  open   dsc
3766/tcp  open   unknown
3998/tcp  open   dnx
4002/tcp  open   mlchat-proxy
5050/tcp  open   mmcc
5120/tcp  open   unknown
5190/tcp  open   aol
5550/tcp  open   sdadmind
5631/tcp  open   pcanywheredata
5815/tcp  open   unknown
5822/tcp  open   unknown
5922/tcp  open   unknown
6692/tcp  open   unknown
6901/tcp  open   jetstream
7019/tcp  open   unknown
7070/tcp  open   realserver
7435/tcp  open   unknown
7938/tcp  open   lgtomapper
8002/tcp  open   teradataordbms
8010/tcp  open   xmpp
8085/tcp  open   unknown
8194/tcp  open   sophos
8254/tcp  open   unknown
8300/tcp  open   tmi
9002/tcp  open   dynamid
9594/tcp  open   msgsys
9929/tcp  open   nping-echo
10025/tcp open   unknown
10243/tcp open   unknown
10626/tcp open   unknown
10778/tcp open   unknown
12174/tcp open   unknown
16012/tcp open   unknown
18101/tcp open   unknown
20000/tcp open   dnp
20005/tcp open   btx
24800/tcp open   unknown
32768/tcp open   filenet-tms
32777/tcp open   sometimes-rpc17
32783/tcp open   unknown
50001/tcp open   unknown
50500/tcp open   unknown
54328/tcp open   unknown

Huh!? The strangest thing is that some ports that are not allowed through the firewall are closed (like netbios-ssn) and others are open (ftp). In fact, the ftp service is not even installed on my machine.

My ipTable looks like this:

Chain INPUT (policy DROP 531K packets, 178M bytes)
 pkts bytes target     prot opt in     out     source               destination         
 6907  339K ACCEPT     all  --  lo     any     anywhere             anywhere            
 115K   27M ACCEPT     tcp  --  any    any     anywhere             anywhere            tcp dpt:ssh 
42398   45M ACCEPT     all  --  any    any     anywhere             anywhere            state RELATED,ESTABLISHED 

Chain FORWARD (policy DROP 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain OUTPUT (policy ACCEPT 164K packets, 30M bytes)
 pkts bytes target     prot opt in     out     source               destination

UPDATE: my real question is – can I assume that, since the local nmap only shows three services listening, that I don't have to worry about all the extra entries returned by the remote nmap? IOW, can there be other processes listening that were not reported by the local nmap?