The DC pins are typically hermetic feedthrough pins (although not always hermetic). They frequently also incorporate a Discoidal Capacitor for decoupling. Sometimes they're soldered in, sometimes they're laser welded in, sometimes they're screwed into a tapped hole, but they're always intended to be soldered to a wire (usually covered with heatshrink when you're done, gotta keep it tidy!)

As for the ground lug, they're always screwed in because who would want to go through the trouble of laser welding something that has no internal pin connection? I have no idea why they have the little flare at the end of the pin though... maybe it's just to make it extra easy to grab with an alligator clip?