I think Darko's point is that it's not very useful to advertise a game as "may have a DRM-free download eventually, but we can't guarantee it", since the customers who are interested in a DRM-free version would not pick that game in a build-a-bundle if there's only a vague chance to get what they really want. I don't think I agree with that argumentation, but that's how I understood it.
The reason why I don't agree is that bundles are so cheap. The customer who wants a DRM-free download, and buys a Steam game that is advertised as "may be getting a DRM-free version eventually, but we can't guarantee it", is taking a gamle. But the prices are so cheap that the gamble may seem worth it. To prove the point, people who buy games that are on Greenlight, and want them on Steam, are taking the same gamble, just the other way round. And it doesn't seem to affect the popularity of these bundles and games negatively.
I see now, but I didn't mean it as a potential advertising line for future bundles.
I mentioned it because it's the easy_way_out_reply from bundle hosts/ organizers and devs/ publishers I usually get when I contact them to express my disappointment about a game being offered only as a Steam key even though it has a DRM-free standalone version.
Note that they never mean that they might
add the DRM-free download to a previous or running bundle, they always say "for future bundles".
I don't think the Greenlight comparison is fitting. With games on Greenlight, devs usually promise a Steam key and they do so beforehand (it's on the game's Info Card) - the gamble lies with Steam's Greenlight and has nth to do with the bundle in question. In the case of a game that is already DRM-free available but is not offered as such in a bundle, there's no gamble to take because that option is never added afterwards; the only way to get the DRM-free version is to buy it again.
How many bundles did you buy where DRM-free standalone versions were added later on?