In a single word, PERCEPTION. The belief that a sale price is a price cheaper than it was before, so as to imply you are saving money when you spend your money and it's OK to buy today even if your not ready or don't need it because this is the LAST sale you will ever, ever see. Second word, MOTIVATION.
IMHO the interpretation should be, we want to sell you something, so we are going to let you think your'e saving money when you buy what you don't necessarily need, but you are saving money, so how could you go wrong.
The most rediculous SALE that I have ever seen, a bank having a financing sale>
Nothing, absolutely nothing has ever been 50% to 70% off, except mini-blinds and they ahve been up to 70% off for 30 years now.