Yeap, the actual cone is aluminum; it is done so that it is lightweight and moves more freely (less inertia). A well done Aluminum cone can have the same benefits as implementing a phase plug (but without the added dust factor), and without the added ventilation (even though the cone acts as somewhat of a heatsink, it doesn't have too much of an effect.) The heat dissipation abilities of the aluminum cone I would belive are akin to that of an aluminum computer case (marginally better, but nothing to write home about). Although I must say, the metal cones are extremely cold to the touch when not in use (and they seem to get a bit warmer when in use, which is a good thing.)
But the fact remains that it makes the cone considerably lighter, which will improve your mid-bass accuracy.