Lenny: If you are worried about DRM just get it from the frictional store. You can download it from there DRM free as many times as you like.
Vault_Boy: I considered this some time ago but then there was this download service blablah and this passage: "Our download is available for as long as we are around". If I buy there, can I install the game just like any GOG, or is some kind of server activity necessary that might cease to exist some time in the future? Or does this only mean that I can redownload as long as the service exists, just like with GOG?
It's the exact same deal as you get on GOG.
You get a order confirmation code that you can use to download the installer from their site as many times as you want.
The installer is DRM free so you can also make your own backup.
I support DRM free so I bought everything they had on their store which was penumbra series, penumbra soundtrack and amnesia. All three set me back a little less than one so called AAA title at release.
Should they someday decide to put it up for sale on GOG I will buy it again here too.