In the Netherlands you can buy a train ticket for that day or one without a date on it. if you buy one without a date on it you must validate it before getting on the train on your day of travel. The conductor reads the date on the ticket to check it is a valid ticket and then stamps it - this can happen several times, or not at all depending on the length of the journey.
If you do not validate it you will be fined, and possibly removed from the train.
I imagine that Italian tickets are not dated when you purchase them so you validate it for your train/day of travel just as you do with undated tickets in the Netherlands. The conductor then checks the ticket is for that train/day of travel and isn't an old one or an unstamped one which you could re-use.

Now we are switching to the OVchip card there will eventually be physical barriers at all stations which will only open when you scan your card. Since we are still in the transition phase this won't happen for a while.
The Strippenkaart which is being phased out and was used on buses and trams also needed stamping - you could do this yourself or ask the driver to do it - but you there was always the chance of an inspector checking you had done so.

Ooops, " conductor's there to do in the first place."

Hi k9,

>would it be so difficult to date or otherwise mark the ticket at time of sale to indicate that it's valid from point A to point B on a particular date?<

What if I wish to buy several tickets at one time and use them on various dates?