I know it seems weird, but it's pretty much exactly the same structure as phones and email.
It's just, we are so used to phones and email we don't even think about the fact they are federated networks. We take it for granted that phone calls get put through to radically different networks, including landlines, mobiles, satellite phones, ship telephones, aeroplane telephones, sometimes even calls to spaceships.
It does make sense when you use it :)