Companies are shrinking everything like this these days. Sometimes just by tenths of ounces so they can save a few cents. When it's just an ounce or two on a shampoo bottle or a bag of chips, we don't even notice. Check out all these posts on the subject:
http://consumerist.com/cgi-bin/mt/mt-search.cgi?IncludeBlogs=1&limit=20&search=shrink+rayI had all these coupons for "buy 1 get 1 free" packs of M&Ms that I was using at 7-Eleven. Since there were 2 sizes of M&Ms next to each other, I would glance at the ounces to make sure I was picking up the right ones. I think originally, when I first started using the coupons, they were 1.80 ounces, but one day they started being 1.63 ounces. The coupons still worked on the smaller sizes (I bet the barcodes weren't even changed) and you can't tell that there's any difference. They're just stealing an M&M or two from every pack I buy now. It's the new way of raising prices without actually raising prices.
By the way, WHEN I WAS A BOY ( *shakes cane* ) all convenience stores had a choice between 16oz bottles and 20oz bottles of soda. Some even had 8oz bottles. 1 liter bottles were unheard of. And they were all glass. As 20oz bottles became more popular, they all phased out the 16oz bottles. Guess they're making a comeback so they can steal some ounces from us. I haven't noticed any 16oz bottles anywhere yet, but I rarely buy soda.