Customers are absolutely fooled by smaller sizes. I've almost fallen for it myself when a coffee package was reduced from 500g to 450. Thankfully I noticed the price per kg was off, but without it I wouldn't have noticed.
This is often done by products using alternative packaging schemes that are meant to evoke personality or authenticity of the food. There are many ‘organic’ brands that sell milk in nonstandard packaging that appears to be a gallon or half gallon but is 10-20% smaller.
