by chance a friend was wondering the same thing last weekend when we were in one of the Apple stores in Los Angeles. She asked and was told that they only carry the base configurations. She then asked if other Apple stores in the area might have other configurations in stock and was told that they wouldn't. The salesman said she could go to one of the authorized resellers and that she would be able to find one that would install an upgrade hard drive into one of their stock configurations for her.
would that end up voiding the warranty? would it cost the same as getting it upgraded by apple?