Pricing is always a challenge, isn't it. Square inches vs united inches is interesting: a 10x10 piece is 100 square inches, 20 united inches. A 2x50 piece is also 100 square inches, but 52 united inches.
But it goes on: A 10x10 piece of glass (or matting) can come out of an 11x14 lite, but a 2x50 piece must be cut from an oversize piece. (most shops special order anything over 48, some anything over 40, and I can't say I blame them) The extra hassle and waste has to be taken into account.
When you have a price chart that goes by size, the labor on a 2x50 piece comes out a lot higher than a 10x10, even though it is only a little more work. Some shops use either united inches or overall size, whichever seems "more fair". Where I worked recently, we had a price chart with an extra column for narrow shapes. This allowed for a some lower charges on 12x36 pieces than on 24x36 for example.
The truth is, it doesn't work to use the same method for every aspect of framing. I sell a 16x20 piece of fomebord as a quarter sheet, (which it is) and divide the price of a whole sheet to get the price. This is profitable and fair. It is also different from the shops down the street. All these differences make it hard for customers to price comparison shop, and they get frustrated.
But, I don't see any way to standardize the process, short of all becoming Larson clones.