They’re not even the same currency at all, yet Steam or any other digital storefront decides to price a 80€ ($91) game the same as a $80 (69€) one when the conversions in reality are different to what the algorithm suggests. It’s reflected on Steam DB that Euro has a higher markup in comparison to US Dollar because of this, since I hear EU players nagging about paying 80€ at launch the same as US players don’t like paying $80.
All prices are set to what people are willing to pay
But for physical goods, the minimum price is what the store paid for acquiring or producing it in the first place. That isn’t a consideration for digital goods.
Its less of a consideration, I would say the cost of selling a disc based game is not a hugely different cost to selling a digital game for major players in the industry
A disc as well as its packaging still cost money; also, a physical store needs to pay rent and salaries.