While its true that there a 4 core is probably the suggested minimum and decent 4-cores will still do well (subjectively, depending on what you're definition of playable and enjoyable is), a higher core count CPU currently is objectively still gonna give better performance than said 4 core. It's especially relevant in the minimums rather than straight averages. Yes its true, above 4 cores start to hit diminishing returns, but we've hit the point in games where for a lot of people, it's already worth it.While I don't play every modern title I have yet to find a game that doesn't run well at 1080p maxed out on my 4670K, including Rage 2.
As I said some titles will benefit as will multitasking but straight gaming is still heavily IPC and frequency dependent and will be for a few more years.
One could probably still make dual cores with HT work and say that its better fps/$ and still have a decent FPS, but we're well beyond the point of that being the generally agreed upon sweet spot. Starting with this generation (a big generalization, i know) of software and hardware, unless you want to actually compromise your performance now and for the coming future, a 6 core or above makes more sense.
That said, a 4 core is still a better value for gaming.