Man try to be realist in a game like this is just... funny. i dont know, if you want to proof with teorys the fact of there arent many robots, but you can proof anithing whith teorys. and with cold abstract. so say "no because its imposible" is only a very useless way of dont let this game have big diversity.
this game is completely unrealistic, and this is the way of fallout
also if you want a really big and awesome history, and everything fixed, its imposible, fallout WASNT MAKE BY PROFESIONALS WRITERS, it was created for a lot of programators that want to make a continuation for Wasteland, but they couldnt because Activision have the copyright, so they create Fallout.
And the FalloutBible isnt perfect but is all we have, the games arent really precisely, and there are many inconsistences, but there are always inconsistences, (awesome games like very artistic creations like Halo or MassEffect have inconsistences between secuels and thats no matter for the canon)also fallout bible is continuing in New Vegas, yes i know NV its not a very good game but its the continuation from some programer and he was there since the begin
also if you read cientifiction you will find reasons for robots in the streets of the ruins, and im not mean actual cientifiction, im talking about the 40 or 30, and fallout is based in this, there are a lot of poetic histories about robots in streets after the human go to hell, living, surviving and dyng, and there are robobrains, BRAINS human brains, they could have consience, they could know the actual way, they could fight for survive, they could enjoy the big pleasure of cut the head off a enemy.
So roleplaying talking robots will implement the actual pve combat sistem, then we should create a good story for put them into the cities and voila good fighting, thats the purpose of the game, the fight
maybe my english is not good, but i hope you understand