Quote from
http://www.toandfromtheairport.com/rome.html
Because of the difficulties of getting tickets at the Rome 'Termini' and the city in general, you are advised to buy your return ticket here at the same time. They are usable for both directions with no apparent expiry date. BUT DO NOT VALIDATE THE RETURN ONE NOW.
I thought it sounded a bit odd, hence the post.
Yea, thats pretty ridiculous. I don't understand what is difficult about it. Never caused me problems.