Thanks for your reply
The game is always yours and if you lose the disc there are no worries as you can redownload it at any time.
To turn this around: If I DON'T lose the disk, and want to play this in the future when valve/steam decide they are no longer supporting this game or are no longer in business, then I cannot activate the game, correct?
I prefer the responsibility of ownership to be with the person that purchased the game, and not with the provider. This sets a dangerous precedent. Would you be happy calling the bookstore before you could open the new book YOU JUST PURCHASED? I think not.
My point is not to be argumentative. It's this: If I pay FULL price for a piece of software, I want to be in FULL control of WHERE and WHEN I install it. If these two criteria aren't met, I feel the seller can't expect me to keep MY side of the bargain either.