Unfortunately Silver is expensive. And copper costs a pretty penny also, and the copper heatsinks out there have soldered fins, which adds thermal resistivity = bad. So while you and me may want a silver heatsink, they are too expensive and the copper heatsinks aren´t perfected yet, so what are we left with? Aluminum! Every other heatsink out there is made of aluminum, cheap abundant and easily moldable. So now that you have a choice of 20 heatsinks to choose from for your Socket A cpu, which do you want? You want one that cools your CPU the best. And it has been proven again and again that surface area of a heatsink adds to better cooling.