You may have expressed your sympathies for the NPCs in your favorite MMO. They never get to leave their shops, and their families miss them. Perhaps they do not even have shops, eternally standing in the sun and the rain in the hopes that someone will come by with frayed rat tails to sell. The lucky ones get to wander along a track, but most of them might as well be vending machines.
Borderlands takes that step. Shopkeepers? You can meet both of them, but mostly you deal with the vending machines they set up around the world. Drop your money in and grenades come out. Drop your sniper rifle in and money comes out.
How does that work? In a sci fi setting, you can have good computers in a box that huge. How do they empty/restock them, how did they get them in these forsaken corners of the world, and why don’t they get robbed? Look, this is a game where shotguns can fire electric rockets and pistols can generate their own ammunition. Being nitpicky about vending machines will not help you when you want to set fire to the acid-spitting dog-thing.