I called a local Apple Store today and asked if they had any 4GB MBA models in stock. They said no, but I could buy a 2GB model and they could add 2GB at the store in like 20 minutes. I could just be slow today -- but how are they doing that? Are they doing on-the-fly memory soldering or something? Is there 4GB already there physically and they are just activating the extra 2GB somehow? Or were they just wrong?