W GamersGate jest tak samo jak w GOG. Będziesz miał konto, na którym będą widnieć kupione przez Ciebie gry, które będziesz mógł w każdej chwili i ile razy chcesz ściągnąć. Natomiast Back in Action i Crossfire będziesz miał w postaci klucza, który musisz aktywować na Steamie i potem z niego ściągnąć grę i zainstalować.
GamersGate sells digital downloads only, we do not sell or ship boxes. After buying a game, it gets added to your account, and you can then download it as often as you like. Some games - as you already noticed - come in the form of keys for third party services, like Steam. These games can't be downloaded from us. Instead, a key for this game will be added to your account, and you can then enter this key in the third party platform (like Steam), which will then take care of the download and installation.
With regard to the "Jagged Alliance" compilation: Some of the games come as Steam keys, some are DRM free. The DRM free games don't require Steam and can't be activated on Steam, you simply download them from GamersGate's servers. To see whether a game requires Steam, please take a look at the section labeled "THIS BUNDLE CONTAINS THE FOLLOWING PRODUCTS" in the page you linked to. This section contains clickable links to every game in the compilation. On the product page of each game, you can check the game's specs to the right of the game's description. If a game requires Steam, then this will be mentioned there.