I didn't do anything wrong, but I did clear my package cache 271kB is in your case the size of the Packages files that were updated - it obviously doesn't download what has been downloaded before (if you did apt-get update again, it would say 0 bytes). In some setups, apt would get DiffIndex-es to cut down on size - but this does not help much in a global appstore context, where you have, say, at least a 1000 new packages a day. If we used metadata Maemo-style, the AppStore's Package files would be around 10GB.

I believe that project wiped out half of the world's puppy population singlehandedly