Faithful: I simply go by the term Digital Rights Management. Anything that Manages your Rights to playing the game is DRM or Copy Protection. So, while most say Impulse in not DRM it does Manage your Rights by forcing you to install an application to update/patch your legally purchased software. It is a soft form of DRM, but make no mistake it is DRM.
DRM is not copy protection; heck you can copy your Steam games or your i-Tune movies 2'000'000 times if you want without any problems... you might not be able to play them but nothing prevent you from copying them as much as you want.
And on the other side Copy Protection is not DRM, if you have the game with the original CD you will be able to play the game forever (as long as you have compatible hardware of course) without the right owner being able to do anything about it.
Like it's name indicate DRM is all about giving the copyright owner the ability to manage and decide which rights he will temporarily grants you, under which circumstance and for how long.
If tomorow Valve decide to remove you access to all your Steam games they can (technically at least), if tomorow Bethesda decide that you no longer have the right to play the retail version of Fallout 3 (protected with a simple CD check) there is absolutely nothing they can do about it.
That's a big difference, that's the reason why some peoples like me can tolerate a standard CD-check (as long as it doesn't destroy their computer) but are 100% against DRM.
Concerning Impulse, well technically Impulse is not a DRM otherwise you will have to consider GoG downloader as being a DRM too.. however most of the games sold on Impulse contains DRM be it Goo, Stardock "nameless" DRM, or others. But you can find on Impulse some 100% DRM-free games (Braid, Puzzle Quest, etc...)