May want to contact both Steam and D2D about that as both have been 'lazy' in the past about listing DRM.
No, D2D very specifically list it as one of their DRM-free games (these work the same as a GOG game, but without the slick installer, just whatever the developer uses for an installer), with a special "DRM-free" logo on the page, too.
And I really doubt the indie devs purchased and mandated Securom for the other sites -- I think they just are using whatever each service's default favourite DRM is: Steam is Steam, Impulse is Impulse GOO, and GamersGate is Securom (they've used it on other titles as a default DRM before, even when other services didn't).
EDIT: But even though I doubt it's the case here, I know what you mean. Borderlands is the latest example on steam, and even worse than usual. When it was first released it didn't have any (3rd party) DRM, just like it says on their page, but then they went and added Securom in a mandatory update, and still haven't updated the page to mention it's included.