The actual reason to finalize this version is the heavy efforts for releasing new version every two to three years. It does not mean that changes and updates are not expected but this is the actual thing that has been decided. Microsoft decided to make updates and improvements in windows 10 every time there is a need for it instead of launching new version.
Strategy of launching new versions every few years is now considered a past strategy. The idea is to launch a good final version and make constant updates according to changing demands of customers. IT field is changing rapidly that demands constant focus and attention to keep the product up-to-date. Windows 10 updates will be ready and downloadable to make the things even more easier and straight-forward.
After the craze of smart phones and tablet PCs Microsoft has been busy to design a windows version compatible to all type of new devices. Now you people can easily think what actually Microsoft is going to plan. Microsoft wants to make windows 10 great enough to be loved by everyone and to make it compatible with almost all type of new devices, tablets, smart phones and hand-held PCs etc.