Quite the opposite: you can
buy regional tickets, unless it's something special.
holiday to outer space on the famous Alitalia bus to fco!
In the Rome's area 'special' means FCO: in this case, you have to buy the 'special' ticket and then add a regular ticket.
Eg, FCO-Ostiense, flat fare € 8, then Ostiense - X. No FCO-X ticketing available. Actually you can see the routing & schedule but you cannot complete the booking.
It's Trenitalia, you know, by the time their IT will deliver this sort of service, I'll have got a nephew who will be able to go on holiday in the outer space.