NPC's can't compliment you on an excellent tactical maneuver, then turn around and use it against you.
but they don't call you a "ZOMG! H4X0R!" or "LOL NUB", and usually have a readable grammar and spelling, well if we don't consider Fallout 3 /kidding
i don't blame you for not liking singleplayer games, but sometimes i just want to relax or blow some steam off, and usually i don't want someone around; i just want to immerse myself in a well written story or have a nice challenge. don't get me wrong i like multiplayer games too (i'm quite fond of Team Fortress 2, and i'm consider gettin Left for dead too), it's just that some games work best in singleplayer and some not.
Also there are rumors that Interplay will bring out a MMORPG version of fallout, so maybe you're more appealed by that one