I also recently lost a season ticket - in my case somewhere between an on board check and home although I suspect it was in the putting away after the check.
In my case though it was a 7day so the loss is better and worse. Better because this isn't the ^1000s for an annual but worse because there are no replacements and if you are lucky enough to have it handed in then it will probably get back to you after the 7days! What is most annoying to me is the lost photocard

As for ticket checks... I have never been asked for the photocard because I always present that for inspection anyway. However I have heard somebody asked "and may I see the photocard for this?" during an inspection. On the other hand a friend of mine presented a season with photocard during an inspection once - the photocard was in one of those ticket wallets and had a collectable football sticker over the photo. Despite the player having a very different skin colour to my friend the inspector thanked him and carried on his way..!
Smart cards seem a utopian future, I cannot wait.