Actually, his main concern is that book prices continuing to be low impacts the ability of game designers to be able to make a living.
Truthfully developing RPGs is a horrible business to be in. The truth is that RPGs are just an incredibly cheap hobby. Once someone has bought the core books for a system, there really isn't anything more you actually
need. You could maybe buy one or two adventures per year, but lots of groups never buy adventures.
Some companies, and WotC in the past, try to make money by selling lots of spat books to players, but that is ultimately a loosing proposition. The splat book churn of 3 and 4e suffer from massive diminishing returns. Each slat book you release leads to fewer sales than the last one. Ultimately people only need so many books. This leads to the edition churn of 3 and 4e. Because each additional book you release costs the same to produce, but brings in less and less sales, eventually you need to throw everything out and start over.
The splat book churn is also incredibly brutal on your employees. How many people remember WotC annual round of Christmas firings? Because each book brings in less money, eventually you need to start cutting staff to remain profitable. Say what you will about 5e's slow and steady release schedule, but it does provide a lot more stability and security to WotC employees.
I just want to point out here that I think there is only 1 rpg company from the early days that hasn't gone bankrupt, and that is Chaosium and Call of Cthulhu. The way they survived is basically WotC's evergreen strategy. Releasing the same game with slow iterative improvements. Seriously look at all the RPG publishers that went out of business, TSR, GDW, Fasa, White Wolf, West End Games.
