I don't think this will follow long term. The lack of predictability of the "casual" market is mostly a consequence of their newness.
In the late 70s / early 80s, as today's "core" market was just being formed, we also saw a lot of churn and a huge amount of unpredictability. Companies like Collecovision, Intellivision, Sears, and of course Atari rose swiftly and then collapsed in to nothingness. As time has gone on, however, companies have figured out what people want and the market has become more solid and more predictable. Churn slowed. Sega was the last real victim, and since that point we've had the same 3 major competitors for nearly 15 years. The market is now highly predictable and very solidified.
Most markets start out this way. The market for soda was not always just Coke and Pepsi; it gradually solidified around them over the course of decades. We can see the market for Android phones gradually consolidating around winners (especially Samsung) right now.
"Core" and "casual" are descriptive, not prescriptive terms to me. Grandma playing Crusader Kings 2 doesn't make CK2 a casual game nor does it make Grandma a core player. Grandma seeing a game about kings and maps and buying a PC to play it, then never really playing any other games for seven years makes Grandma a part of the casual market. The same result would apply to the 23 year old super nerd who listens to Dream Theater and has the same player/buyer patterns.
The console market in the early 80s waned but the PC market was fine. The core players went where the games were. They were repeatable, even then, only smaller due to awareness (you can't know if you want to keep playing games if you've never played a game before).
I think you're more in tune with innovations inside genres you already like or are already familiar with. The differences seem particularly pronounced and important to you, similar to how small changes in the sound of a band may seem like a huge departure for a fan of the band but may sound identical to someone who isn't.
That doesn't mean that the genre didn't change at all, mind you. It did. I'm only examining the long term economic trends here.
I'm going to assume you mean "one is more in tune with" rather than directly me, as I don't think I've ever played a CoD in my life.
The differences are irrelevant, I'm only looking descriptively at the results: CoD4 had something in it (whether it was innovative content, a level of polish, subject material, whatever) that became a flashpoint for growth. That growth was in a well established genre that consistently sold well before, but became a zeitgeist with this particular installment.
I'm just pointing to the idea that saying you need to branch out from a particular genre set to create growth has had exceptions in the past (in 2007 alone, there were multiple super successful FPSs).