What confuses me is the UI changes every version. If Microsoft's bread and butter are "casual" or "clueless" users, aren't they vulnerable to changes much more

What confuses me is the UI changes every version. If Microsoft's bread and butter are "casual" or "clueless" users, aren't they vulnerable to changes much more than power users? Maybe M$ PMs don't care about confusing your average grandma who can't find the start menu because it moved to the middle of the taskbar. It's not like granny is going to up and switch to a Mac, is it?