- It makes no sense to increase ram (expensively) by 4Gbs and then reserve 3 for the OS.
- the OS will have been designed back when they were only expecting 4GB and therefore will be designed to be fairly lightweight (rumours were 512MB). Now they might increase that to 1Gb which - compared to before - would give them reasonable headroom just in case *and* the possibility to reduce it if it isn't needed.
- what the hell is MS needing 3Gb for anyway!? Maybe windows running in the background, but we don't really know. You really don't need that to run apps in the background. WiiU has 1GB and can run a full, decent browser in the background. PS3 has around 50MB for the OS but can download in the background, record TV shows via an accessory tuner in Europe and Japan, and remote play games to PSp/vita.
-It makes sense to increase the RAM to counter what your competitor is doing. Do you have any doubt that the PS4 would have 4 GB of RAM right now if Microsoft didn't have 8? Knowing that Microsoft is going to place a heavy emphasis on applications, services, and multitasking, it makes perfect sense for Sony to respond by ensuring that their system is capable of competing with their primary competitor in that area. You would see diminishing returns in games with 5GB vs. 7GB of RAM, but by assigning more of the added RAM to the OS, they are giving themselves more flexibility, and making certain that they are technologically capable of countering Microsoft's offerings. Basically what I'm saying is that the extra 4GB of RAM was added to the PS4 in response to competition, and know Microsoft's strategy, the most valuable allocation of that memory to address said competition is to give a fairly large chunk of it to the OS.
-I doubt the OS footprint itself is very large. I think the primary concern is running other applications and services while playing games. For example, if you want to livestream, chat with your friends, and use a web browser all without quitting your game, it starts to add up. Also keep in mind how Sony emphasized that they want to eliminate the time required to start up and play a game by preserving the game state in RAM. In this case, all of the other OS features (like listening to music, watching video, viewing photos, using the store, etc.) should be available while the game is still in memory. All of this still wouldn't add up to 3GB (although probably more than 1 GB), but it makes sense for them to keep their options open for more memory intensive applications in the future, knowing that Microsoft is positioning themselves to do so.
-We don't really know what the specifics of Microsoft's plans are, other than that they will likely have a focus on being an all-in-one "entertainment hub." My guess is that they simply want to leave ample space for seamless, fast app usage that can run while a game is in memory.