Respectable stores like Steam will warn you about the types of DRM used by the game in clear terms
Steam only warns about the additional/external DRM, not about itself. There is no "Warning: to play this game you need to be logged in on Steam and have the game fully updated"
A very large reason for this is the fact that it's rather obvious that you need to have Steam running and be logged in to play.
Only obvious if you've used steam before, as someone who pre-ordered half-life 2 and couldn't play it for nearly a week after receiving the disk (had to pull my desktop over to a friend's house to activate it, as my internet was too slow)..no, it was not obvious that i needed to be online and signed in to play the single player.
For people saying "but there's an offline mode!" , you can't set that while your internet is down, you have to set that while the network is up and you're still connected to steam, and your games on initial activation force the patches immediately, which is fun when you have a 5GB a month download cap.
I fixed that though, since i already owned a copy and couldn't return it, at least i grabbed the pirated copy that doesn't need steam at all to play (the crack was out well before steam even became stable), but I never have, and never will buy or pirate a game from steam, or from valve at all, again. I still have my original install disks for half life, op4, blue-shift, tfc, counter-strike, etc.. so at least i can still play those to some extent. (local multiplayer at least for TFC/CS)
and a modern PC it doesn't matter at all.
This is EXACTLY why we have to constantly buy new hardware, and upgrade the CPU/RAM to do the same exact tasks were were doing with 1/100 the power 5 years ago....