I personally wouldn't get a game i can get without Steam on Steam, which i consider is the most retarted creation in the history of comps.
I personaly dislike Steam, it literaly tethers your game to having access to the internet. I have been playing games like Civ and other such game perfectly fine without Steam. My mom who has been playing Civ since the first one back in Ukraine, cannot play Civ 5 because she doesn't have a internet connection on her desktop at home and cannot install Steam. She doesn't need Inet there, and if she needs a quick access she goes on the laptop.
Games like CoD, CoH, Red Orchestra should not be bought off it, but so many good games are thethered to this useless service. I would much rather walk 2 miles or get in the car and go to the mall to buy a PC game on CD, it takes forever to download a game esppecaily the bigger ones, where if you have the disk it takes a max of 2 hours (depends on game and comp of course). With this crappy service I am forced to attach it to Steam, and i need a inet connection to get on and play Napoloen: Total War, Left 4 Dead, Civ5, and the list goes on. Great games, but perma-attached to the Inet. Not everyone likes listening to noobs whinning. Plus the Valve anti-hack system isn't as reliable as Punkbuster or other such more efficeint software.
The bonuses of it are the community. Can't say i see any other ones