Like all surveys and data, this is pretty skewed (especially if the criteria is ONLY PC/Mac).
A vast number of female gamers play portable games, for instance, with a nearly 50% split in RPGs like Pokemon between boys and girls. Are they not considered "core" gamers despite the hundreds of hours of playing one of the most hardcore genres?
So it's a weird and narrow survey, insightful though it may be.
Though, honestly, I find the "problem" two-fold. The first is that continued need to be exclusionary towards other forms of gamers other than "core". It's a strange term, just like telling people who watch and enjoy movies they aren't "core" movie watchers if they only watch a movie a month instead of a movie a day, or people who enjoy TV shows instead of film, or people who watch on Netflix instead of the theater. The criteria is strangely limiting in that regard, just like picking only one platform to survey on.
And the second thing is that, yeah, "core" gaming is still universally marketing to boys, so even female gamers that enjoy gaming are just not important as as marketing demographic (despite the fact my love life was forged in the 90's in the arcades by impressing folks in Mortal Kombat...).
I mean, I know I'm biased because I play a HUGE variety of games (everything from platformers to puzzles to strategy to survival horror to adventure to RPG to shooters to fighting to everything), and yet I've often been said I'm not a "core" gamer because I don't play Call of Duty on Xbox... which, to ME, is the most casual game this side of Farmville, Minecraft, and Angry Birds.
There are people out there who ONLY buy Call of Duty or Madden, and nothing else, and they are considered "core" gamers while someone like me, who due to the realities of life and jobs has limited time to game, but plays and enjoys games like Okami, ICO, Shadow of the Colossus, Bioshock, Xenoblade, Zelda, Blazblue, Silent Hill, Psychonauts, etc., is often excluded from the surveys and demographics because I don't like or enjoy THE most popular and mainstream FPS on the market.
Ultimately, it's semantics, but my final thought is that, for an industry that so often self-implodes, budgets go out of control, and they water "core" games down so often to reach a wider audience, the fact that including women in the discussion or playable releases (hello Assassin's Creed Unity) isn't a priority for the vast majority of developers, despite being a thriving, growing, passionate demographic, is shocking to me.
For all the crap I give Capcom for their terrible business decisions, I can still look at a popular game like Street Fighter IV and see men, women, young, old, black, Asian, Native American, big, small, spiritual, rich, poor, gay, straight, even hermaphrodite characters in the game... and, shockingly, people seemed okay with this and the game is still the most successful fighting game in the genre last console generation.
I would kill to see that same variety in a shooter.