It's probably more like they get better margins from digital sales, so they want people to go digital and this sweetens the pot a little bit. 10% isn't much, but it's not like they can resell the game. They just want you to put it forward towards a new game/DLC to make their money back.
They pay you to deactivate your game license, so you put that cash towards a new license for something else.
10% is low, but it's better than nothing, which is what you currently get for used digital games on all platforms.
That said, if I had to make a guess, the only reason Microsoft is even considering this is that they haven't given up on their all-digital console dream.
They're looking for the price at which people will except an all-digital, no-used-games Microsoft future, since the ability to sell used games is what people fought for the last time Microsoft failed with this push.
My guess for the way Microsoft wants this to go? They figure out a price for digital "resale" they think most of their audience will accept. They implement this price for all digital games you buy on Xbox.
Then at some point during one of their ".5" Xbox cycles, once they have introduced their yearly new models or whatever, they introduce an (optional) Xbox model that is all digital games, at a cheaper price. You save money on buying the box, but don't worry about the fact that it's all digital, because you can still "sell your used games" back to them. Hopefully, in Microsoft's eyes at least, this goes over fairly well, and two or three product cycles down the road, suddenly all the Xbox models are digital only.
People that buy Digital currently get nothing for the games they've finished with but snob 10% cash back? I can understand it's pretty low, but if you have 20 games that you've bought digitally this gen and no longer play then that could be up to $120 back.
I'm not defending it, I'm against digital as it is and have only bought one retail game digitally on consoles since it started and that was GTAV on PS3.
It almost doesn't matter. At this point they have primed the conversation around the 10% price point. Then, when they come back with something slightly higher, people will be like "oh, alright."
This is already happening for some posters in this thread, who have already stated they would be willing at 20-30%. If MS came straight out and said 30, people might have pointed out how low a number that is, since "you don't even get half". Now, 30% looks like a luxuriously high price point compared to the 10% they were originally thinking of, and Microsoft gets to look like they're being the good guy by giving you "so much" for your digital games.
Would be more interesting if they would allow used sales to other people directly through a online marketplace. Have people bid on the game and see how they value it. Publisher takes a cut to make it interesting for them.
I think it' safe to assume that there will be plenty of restrictions. Another loophole is if you bought a game and then it's later offered as a GwG game. Every person who bought the game digitally would sell it back. That would literally cost MS millions of dollars.
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