It comes from having a controlled environment to develop for. A console is a console is a console. All of them have the same latency, bandwidth, and access time in regards to their optical media access (as well as being identical in every other area). PCs do not have this level of uniformity.
They are not exactly the same in architecture or performance. For one thing the 360 uses video memory also as system memory. Video memory is a lot faster than the system ram we use in our PC's. If they were the same then we would be able to play games straight from optical disk without pauses and stuttering like a console can. The PC can't do that.