What is required for a game (engine) to support multi GPU(s) systems (because it suppose to be quite

[Calin Banc]

Although a lot of games don't support this or the scaling is bad, it seems our friends at Bohemia consider that having SLI or CF in your game is quite easy: http://steamcommunity.com/app/107410/discussions/0/458606248620063074/#c458606877322824034

game developers do nearly nothing in term of support for Crossfire and SLI
(at max they need properly detect GPU memory available as it's not shared)
everything else is left to IHV's drivers ... in future this might be in hands of DX12+ / Vulkan

Any comments on this? Are the devs that lazy to not offer proper detection for the vRAM in games where this technology isn't usable? Are AMD and nVIDIA that lazy/indifferent to offer support in drivers or the above is just standard PR talk?