Pretty common. Hitting price points is important for groceries, an item selling for $2.99 will outsell the same item at $3.09 by 10-1. If a manufacturer can't hit a target price anymore they downsize the product rather than raise the price. Take a look around a supermarket, especially at stuff in cans. It used to be that all the canned veggies, fruit, dog food, prepared foods, coffee, etc were all 1 lb. Now almost all are 11-13 ounces.
You can work that to you advantage if you know what's going on. Supermarkets will often advertise their sales based on product weight like "Half gallon ice cream: $2.99" or "13oz Alpo 3/$1.00". If the product downsizes and they advertise the old price they're sort of screwed because they have to honor the published sale price. Take a 1.75qt container of ice cream to the service counter and demand a half gallon like is in the ad. Have fun watching them try to solve it. You can probably get a free container out of the deal.