Two things...
1. APU... the Xbone APU is close to 50% bigger than PS4 APU and it is more complex... so way more expensive.... and there are relates about low yields (that makes the chips over more expensive).
2. Kinect.
I think I covered everything.
To be fair... the GDDR5 on PS4 is more expensive than DDR3 on Xbone but I think the APU difference is bigger than GDDR5/DDR3 and there are Kinect to add to MS costs.







