Steam games launch as expensive as the retail counterparts because big chain stores like Gamestop Target and Walmart refuse to stock it if its launched digitally for less money. Also, there is no reason not to launch a digital product at an extremely high price point, because if you can get someone to buy it at $100 that is just $99.9 in profit.
If you are selling the game in stores, you have to pay for polycarbonate disks, the plastic packaging, shipping, stocking, store fees, you have to play international politics wherever you are selling it, you have to put up some advertising on site for the game, and that all does cost an actual sizable amount of money per copy compared to just having an FTP server grid pushing out copies of the game to people that clicked a button.
If the console market went pure digital, their per-unit costs would go to $0, so they could sell their games at whatever price they'd want, and fluctuate the price however they want. The shelf price can't change much besides slow discounts over a stock time and most games go off the shelves before they'd see any real discount. Online, a publisher can flick a switch across all distribution channels on what to sell the game for (assuming steam / gog / etc lets them) and have a new price overnight.
No, you can't assume a publisher would ever cut the cost of the game, but these people are in the business to make money and surely someone in each of these companies understands that to profit maximize they sell early for a lot and drop the price over time to get the most money out of the most people.
The only curveball in digital distribution to contend with is that you are always competing with free, because thanks to bittorrent someone else is always willing to send you the huge multi-gigabyte number of the game and pay the electric bill to transmit it. That naturally drives prices to $0, or in Steams case around $2 - $3 even for huge titles from 5 years ago.