Before the days of games being forced to include a multiplayer mode only to flimsily justify a $10 online pass, video game companies and video game retailers appeared to get along. As the only way for distributing their game, maybe video game companies had to get along with video game retailers, but that all started to change in 2004 with the release of Half-Life 2.
Not only was Half-Life 2 almost universally acclaimed, but it was the first game that used Valve's Steam software, which meant that it was the first game to be sold entirely through digital means as well as through retail outlets. Not only did the release make retailers rich, but Valve received direct profits from all of the people who bought Half-Life 2 digitally. Over the years companies started to notice and acted accordingly; more video game creators tried to strangle their customers to online systems to have more control and income while video game retailers started pushing used sales to the point where their profit comes solely from the used market. However, it seems that the war between video game creators and video game retailers maybe coming to and end.
According to Kotaku, a source that works for/is an insider of Gamestop states that the video game retailer is planning to start selling Steam vouchers on May 15th. Apparently buying Impulse didn't help Gamestop too much in the digital distribution space, which is why Gamestop might be going down this route. Assuming that this rumor is true and that the vouchers will work like a code-based version of the Steam Wallet option, here's how everything will hypothetically work; you will be able travel to your local Gamestop, buy any variation of the voucher at the retailer (currently the only Steam Wallet functions are $5, $10, $15, $25, $50, and $100), arrive at your house with your computer, enter the code that's on the back of the card into a special "Enter You Code Here" box on the Steam wallet page, and redeem the $X into you Steam wallet.
Of course, the process could be completely different, but I don't imagine Valve would make it any harder as Steam is a very convenient software already and doing anything to go against that would be violating the entirety of the program.