It is more difficult to forge a stamped receipt, true. As to whether it proves that you purchased the item is debatable because both a receipt and a stamped receipt can be easily forged. The question is: is it necessary? Tally up all the man-hours a country spends stamping receipts. Could that time be put to better use? North America seems to function fine without them. Perhaps we've come to realize them as redundant - or are we too gullible to not demand rubber stamped receipts in the first place?