read this at the areats summit...
"Normal items add the max number of Sockets depending on the item's level (this is determined by the level of the monster that dropped it) and the inherent maximum number of Sockets for the item's base type. So you may not always receive the "max" number of Sockets"
so if a low level monster dropped it there is a chance of it not getting max sockets, but i guess cows are high enough?