I may be wrong, but in reading the original post, I made the assumption that the question asked leaned more towards Is there a need to have a firewall installed. The proof of concept is under the premise that the your system is hardened by you, who by the way is experienced in computers, networking and the such. I really thought the original question pretained to the average joe blow's system and not just your system.

Now, if the question is do YOU need a firewall, my answer would be maybe not.

If the question is does the average user need a firewall, the answer is by all means yes.

I'm feeling that the proof of concept here is slightly biased, because the given is the user knows how to harden their system.

I think the proof of concept should be based on the average joe blow user who just bought an emachine from Best Buy and installed DSL yeseterday.