The key is taking small incremental steps, such that the end (large) result isn’t a surprise.
Windows 8 has found this, with the big step up from Windows 7. Trying to bring the touch screen interface across both platforms (mobile & desktop). Users have struggled, the start menu is gone, it’s been too big a leap.
Whilst yes it is overdue to update – people rely on their desktops each day. When you significantly change that it makes them uncomfortable.
It would have been better, to keep growing the desktop experience and changed consumers perceptions with it’s tablets. Then keep up the updates. I think Apples on a good track to doing this, each year they’re releasing small incremental changes – slowly but surely working towards a significant change.