I can't vouch for the Creme Egg thing because I don't eat those anymore, (Devil Woman gave me Diabetes!) but things have been shrinking and costing the same price recently.
I was let down back in the late 90's that soda distributors stopped selling six packs of 20oz bottles of soda at grocery stores in favor of the 16.9 oz bottles. You can still get the 20oz bottles at gas stations and 7-11's, but they are more expensive, and are singles rather than six packs. They call the 16.9oz bottles half-liters (I know that's the amount for the half liter) and charge the exact same, or more, for a 6 pack of half-liters than a six pack of the 20oz bottles.
I've also noticed that if the size of something stays the same, then the price will go up. I'm a hairstylist by trade, and when I used to go to the distributor, a 3oz tube of haircolor used to cost $4.55 two years ago. That same size tube today costs $5.25. That's an increase of about 11.65% in two years. That's still cheaper than using haircolor from the drug store, and the color results are pretty consistent for the stuff from the distributor. You also get an average of 3 uses out of a tube of color instead of a one off from the drug store color.
I think it's official, the price for something is going up even though we have modern production technology, and packaging; we're going to pay for that as companies use them.
