Being a fan of aluminum for about 95% of my lights, when I first read the topic of this thread I thought "heck, aluminum is better for a million reasons! I'll sure give all the reasons and details in my response, just as soon as I finish reading the OP!" And then as I kept reading down the list of reasons, I realized something: aluminum isn't actually better at all! I mean I absolutely LOVE (and prefer) the feel, look, and "work" of a quality aluminum body of a SureFire for example, but I have to admit the OP made a lot of good points... most of them factually irrefutable indeed. I must admit, I stand corrected, and I am frankly quite amused to say so!
As far as the firearm side of this thread (moderators please pardon the slight step off-topic, I only mean to add insight to the metal vs polymer debate) I wanted to be the first to mention the fact that HK was the original user of polymer in handguns, but GaAslamp beat me to it! To be fair though, while HK was the original/pioneer of polymer, Glock was the first to really mass-produce handguns with polymer frames.
Polymer is just as good as (if not better than) metal in many circumstances in firearms as well as flashlights, but to go into full detail would take me too far from the proper topic. I will say though that there is certainly something to be said for the old-school wood-n-metal battle rifles of the past. In WWII for example, if your M1 ran out of ammo or malfunctioned you could still CRUSH people with the thing... it is BIG, it is HEAVY, and it is SOLID. The same can be said for lights such as MagLites, and for someone such as a Police Officer it is always good to have that compliance "device" either as a backup to your primary baton or as a baton-style weapon. I own a SureFire L7 and while certainly not as beefy as a 3D- or 4D-cell Mag it would be an effective defensive weapon.
For a personal, EDC-type light I can appreciate the many benefits of polymer over aluminum as listed by the OP. While many like myself still prefer aluminum I think I've actually gained a little more appreciation for the "plastics" after reading this thread... learn (or in this case come to the realization of) something new every day, I guess.