This computer is very close to a rMBP, and lets be honest, the display has a higher rez. rMBP is 3K this is 4K. rMBP has a faster CPU option but this has a 960m that's better than the rMBP GPU. So why is it cheaper? Three reasons.
The biggest is that its not using PCIe SSD. PCIe SSD is crazy expensive. If you look for it on amazon the closest one to the 512GB matching the read/wright you can get in the rMBP is $699.
The next thing is that it has 1 more thunderbolt port than it does, that's going to add probably $40.
The rest of it is that fact that its Apple, i.e. design cost. I've said it before, Apple is largely a design company, granted a electronics design company but design none the less. This causes things to cost more than they may technically be worth. However, they look and perform amazingly so that's a conclusion you would have to make on your own
. I bought a maxed rMBP 15in recently, For that same price I could have gotten a PC with better memory, fast cpu, two GPUs that each one by itself is faster than the m370x. But it would have been bulky and not very portable. This PC you listed is very similar to the MBP and the GPU is better. But it doesn't run the Mac OS. If you were getting it for gaming I would say do it, or maybe a similar one as the reviews are not that good. But if this is your main computer, the Mac OS is a large selling point.
The sad thing technically a PCIe SSD isn't expensive at all to Asus or Apple. It is just a feature that sounds flashy and they make it cost. The PCIe SSD should really be the default but in any case it 2000MB/s sounds good but in reality it means very little performance advantage over just a standard sata 3 ssd. It does make much of a difference in practice.