Well if someone is your friend and they exist, I don't see why they can't be your 'real friend'. Some people have autism and are looked down upon by the social groups around them so they feel the need to look for people outside of their immediate vicinity whether it be 100km away or 10,000km away. There are of course other reasons why people would want to become friends with strangers like joining a guild and choosing to communicate with each other outside of the game purely for the discussion of the game at first but then casual subjects which open up a bond.