adamhm: ... unless they clearly announce plans to start supporting it.
Trilarion: They did now. After so many comments this thread can probably rest now. GOG finally listened to the customers and their long time wish.
As a first step they will provide Linux versions for a hundred games DosBox, ScummVM, Native clients in fall 2014 supporting Ubuntu and Mint.
http://www.gog.com/news/gogcom_soon_on_more_platforms I suspect the main reason they aren't doing it now is they need time to train staff and figure out what adjustments they need to make to their QA process.
I think they'll find that in many cases it's not really any extra work to add support. Especially for DOSbox games and ones released that have an official Linux version.
Duffadash: Finally!
Although the move to support Ubuntu/Mint specifically seems a bit weird to me. Surely it would make more sense to use generic FatELFs as Icculus has repeatedly suggested?
Also, it will be interesting to see what games will get Linux support. Obviously most/all DOSBox and ScummVM titles.
All the modern indie released with existing Linux ports also seem pretty sure.
Then we get to older ports, such as the Loki Software games (did the publishers keep the rights to the ports, or did the guys at Loki?), this will decide whether or not we should expect Heroes 3 and Alpha Centauri for Linux.
Then there's the RuneSoft ports, which it seems like RuneSoft have kept the rights to. These include Jack Keane, which is why only the Linux version is available on Desura.
Less likely are the ports with less official support, such as Unreal Tournament, Serious Sam and Neverwinter Nights...
And finally there's CD Projekt Red's own games; The Witcher 1-3 and Cyberpunk 2077.
Anything that Loki has would have been either returned to the publisher or sold in bankruptcy court to pay whatever debts remained when they went under.
Whether or not the publishers bothered to keep the files is definitely something to wonder about. The industry does a crappy job of retaining things that aren't immediately profitable.