Are you saying that, once installed, I could zip up the directory and put it on another machine and be able to run it under a different steam account? (No.. I have no intentions of that, but I'm trying to understand what happens with a Non-DRM Steam application.)
TBH, my best guess is that it will depend on the game...I certainly wouldn't assume that all games that don't use the DRM component of SteamWorks are simply zip-n-play-anywhere. For one thing, I don't know that the actual game installer is necessarily available on your HD when you install on Steam-- maybe certain DLLs won't get installed/registered if you just zip up and copy a game directory.
Further, I'm not sure that "run[ning] it under a different steam account" would actually be DRM-free, since it requires a Steam account and client. I'm pretty sure the anti-Steam folks would say no.
But all that said, I did just zip up two (fairly small/simple) games, copy them to a computer without even the Steam client installed, and ran them perfectly.
I should also mention that, of course, if the game itself has any form of non-Steam DRM, then that will be enforced.