Windows Runtime applications (the new kind of applications) can only be sold / bought through Windows Store (lots of reasons to do that, from security, to reliability, and so on, rather not list them, did a 62 pages thesis on that, don't want to go through the same again :D).
What I was referring to with GOG listing the games in the Store... Imagine a user learns about Torchlight:
1. Windows 7: Searches Bing / Google and gets store listings for GOG, Steam, GamersGate and Torchlight's official website. Where should a user buy the game from? If he goes to a place other than GOG, GOG lose a sale.
2. Windows 8: Same as above.
3. Windows 8: Searches the Store, because it feels very natural to search the officially provided Store for stuff that he wants to buy. But now, GamersGate has actually listed the game there, not GOG, so GOG lose a sale again.
4. If GOG are the first to list the games in the Store, they would only gain sales, at the cost of a company account that is around 100 - 160 EUR per year (can't remember now).