iptables not blocking ports

For some reason, iptables isn’t blocking ports on a droplet, when the exact same rules work fine on a VirtualBox VM. The output from iptables -S is:

root@public:~# iptables -S
-P INPUT ACCEPT
-P FORWARD ACCEPT
-P OUTPUT ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -p tcp -m tcp --dport 22 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 80 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 443 -j ACCEPT
-A INPUT -j DROP

This is modelled exactly on the tutorial at https://www.digitalocean.com/community/tutorials/how-to-set-up-a-firewall-using-iptables-on-ubuntu-14-04, with a small change to the conntrack line due to Ansible’s iptables module kind of doing that whether I liked it or not.

But that’s not a helpful explanation, since the behaviour of the exact same rule set on Debian 8 is so very different.

Any ideas why this doesn’t block on a droplet, i.e., even with these iptables in place, a telnet command to port 554 will connect.