Yes - K-series CPUs have higher clockspeeds than non-K CPUs, at the expense of having higher power draw, and in the case of Skylake, not coming with a cooler.
Only the 4790k, as there is no equivalent unlocked CPU
There is no i7-4790?
It's like it's overclocked from the factory.
Also, why didn't they include their stock cooler? Do the K CPUs heat so much that the stock cooler is inadequate?
No, the older k-parts actually lack vt-d support compared to non-k parts, so it was actually strictly worse if you don't overclock.
most people don't care about vt-d
It's used by VirtualBox. I care about that.
Unless you use pass through its not used. Even in VM its an extremely tiny niche. More importantly you need motherboard/BIOS support for it to work as well.