Debian :: How To Use IPtables - Basic Firewall Setup

Recently I have been working on iptables and trying to understand how to use it. Here's a little script I have written to setup a basic firewall for myself:

Code:
#!/bin/bash
if [ `id -u` -ne 0 ]; then
echo "You need root privilege"
exit 1
fi

PROG=/sbin/iptables
$PROG -F
function sethttp {
echo "Opening http port..."
$PROG -A INPUT -p tcp --dport 80 -j ACCEPT
}

function sethttps {
echo "Opening https port..."
$PROG -A INPUT -p tcp --dport 443 -j ACCEPT
}

function settorrent {
echo "Opening torrent port..."
$PROG -A INPUT -p tcp --dport 52413 -j ACCEPT
}

while getopts "hst" option; do
case "$option" in
h) sethttp;;
s) sethttps;;
t) settorrent;;
*) echo "DOH!"
esac
done

$PROG -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
$PROG -A OUTPUT -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT
$PROG -A INPUT -i lo -j ACCEPT
$PROG -A OUTPUT -o lo -j ACCEPT
$PROG -A INPUT -j DROP
$PROG -A FORWARD -j REJECT
echo "Done setting up the firewall! Enjoy :)"
exit 0

OK, this can take 3 arguments that open ports 80, 443 and 52413. And at the end, some default rules are applied. But here's the thing I don't understand:
if I don't give the argument for port 80, I can still view web pages... and also, when I remove the line:

Code:
$PROG -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

Whether I say it to open port 80 or not, I can't view any web pages.