In the Super NES era, games used to cost $60, which is about $90-something in today's money after inflation. Now in the Xbox 360 and Xbox One era, games still cost $60. Day one expansions make the extra $30 of content optional to buy.
You may be right. There's not really any evidence, but it's a plausible theory.
Here's the thing. The market is much larger now, and the distribution costs have only gone down.
The best selling game in Super NES history? Super Mario World. Copies? 20.5M.
Compare that to GTA5, which has shipped over 45M copies to retailers alone, not even counting direct sales/downloads.
So just the revenue that we have visibility into is 75% higher.
Here's the other thing. If the game needs to be $90 to be profitable, then set the price at $90. Don't set it at $60 and then nickel and dime everyone to death to make your $90, explaining how they made "optional" parts. "See, the book is only $5, but the ending is another $5, and if you want any of the 5 subplots, those are $1 each." At best, it's betraying the vision of the artist for finished product he wants to be seen. At worst (and the skeptic in me says in most cases), it's deliberately gouging your customers.