Considering I read it in my issue of gameinformer, there's an article about it on every gaming website, and MS have all but confirmed it, I say it's true.
I have to correct myself, seems PS4 has 1 GB for OS so 7 GB's for games.
Here was the interview with Marc Whitten , notice how he doesn't deny the RAM allocation question, it was a question that would have had negative reactions from gamers so he didn't say yes, but he didn't say no either, because he would telling lies because it is true. If he could say no he would have, but he couldn't because he is the Chief Product Officer of Xbox One and you don't lie when you have that position.
Game Informer: "My question is in terms of RAM you said there is 8GB of RAM my impression was there is 5 of that being diverted to the games, 3 of that to running the always-on apps partition. Sony has 8GB of GDDR5 which is pretty fast RAM and I think it is all unified towards games. Do you think that puts you at a technical disadvantage because there is [in the Xbox One] only 5GB of functioning RAM for games?
Marc Whitten: "Yeah, Im not going to talk about Sonys system, Im not close enough to really understand how there system works. I will say that I think the way weve balanced our system is really key, in terms of two things. The first one is we believe that we are going to have amazing experiences that are clearly next-gen. I think you guys saw some experiences that set a bar that is clearly very high... This isnt about so I can watch TV at the same time as Im watching games those are interesting scenarios as well. At a gaming level the ability to create a modern gaming experiences, where LIVE and the apps and services you can run at the same time as the game, we think will really change that experience we think its key.