Regarding Steam’s “Save X if you own Y” discounts
In the current Steam sale, Valve are trying something new, where for some games, you get a greater discount if you own another named game (often one in the same series, or by the same developer).
However, it appears that if you qualify for the discount, you can also get the cheaper price when gifting.
If you want to get one of the games that has a potential additional discount, but you don’t own any of the required games, it might be worth canvassing your friends list for someone who does qualify for the discount and is willing to purchase the game on your behalf.

Could you give me an example of the discounts? I don’t notice any.
So far there has been one included in the daily specials of the sale, I think. Today’s is Amnesia for cheaper if you own one of the Penumbra games.
How does it notify you of this kind of deal? As I can’t see anything glaringly obvious. Thanks anyway.
It’s mentioned on the sale section on the Steam homepage.