You have your good point, unfortunately, not all of us born rich. And
most people dont have problem RMAing their products through online retailer. Amazon, for instant, no question asked policy for returning an item, they just send you a returning box with self stamped address so you can send in the returning item. Or in the case of exchanging, they send you a new in replacement of defective item with one condition, you have to send the defective item back to them within 30 days of receiving a new one. In your situation, $20 saving is a small amount. In some cases, buying online saves over $500. For a few dollars saving, of course it is a no brainer to buy in store. but online retails are for big savings.
I am currently eyeballing a 40" sony Brevia XBR LCD screen. In a retail store, this sucker costs $3500. But online I can find it for around $2600 - $2700 shipped and no tax. Thats almost 1k saving = 1 week of hard earn money. And when buying online, I do my research before buying using retail store. I go into retail store to check out the product then I read the reviews online before making a purchase. So I dont have any problems with satisfaction and thus I dont have to run into the hassle of returning.