The curve ball that we just looked into the mitt is: we've always though of leadless leadframe as ... Land Grid Arrays (LGA). An alternative to the BGA for device manufacturers is to package their devices without any terminations on the bottom. Although not technically accurate, the easiest way to picture a LGA device is to imagine a semiconductor with nothing but tiny round gold plated pads on the bottom. (If the device were a BGA, a BGA ball would be soldered to each pad. Another way to picture it is to think of a pin grid array with the pins cut from the package.) In order for LGA devices to get connected to a PCB, there must be some intermediary device with pins, or springs, or something, that can spring up and make contact with the little windows. So, almost by definition, a socket is required in order to connect an LGA device with its target PCB. And continuing with the definition, there must be some kind of cover or hold down mechanism that pushes the little windows of the device against the contacts of the intermediary connector.
... but these critters don't appear to be using "sockets". Hmmm.