re:
It's all part of the auto-increment build number that is built into the Integrated Development Environment that they use to write and compile the code for Windows. It's just been a long time since they first began developing Windows, and every time they hit the button on the compiler to re-build it to test what they have written or re-written in the code, it increments the number by 1. It's taken a lot of years to get over 10,000 builds.