Perhaps laws change by state, but here in Maine, if you buy an item at full price this week and it goes on sale any time over the following 14 days, you can bring your receipt back and they will refund you the difference; you don't even need to bring back the original item, just the receipt. I don't know if this is state consumer law or just good customer relations, but we've done it in a variety of stores:
Best Buy, Sears, the grocery store, Home Depot, Target,
WalMart, etc. They call it a price adjustment.
FYI: Both JetBlue and AirTran gave me price adjustments on non-refundable airfare. JetBlue always does it. With AirTran, I purchased tickets and they had an airfare sale the very next morning. I missed the sale price by mere hours! I called and asked them and they told me that as long as the exact same fare code (can't remember what the real name is, but it had to be same class, flights, dates, etc.) was available, they'd credit the difference to an AirTran account as I'd called within 12 hours of booking. I ended up with $100 credit with AirTran towards a trip within 12 months. Never hurts to ask!