Is there any particular reason for omitting this useful feature?
It is not omitted. Use Time Machine (which is built in to the operating system), or some other backup software which clones the system*:
http://www.macmaps.com/backup.html
Having the user expect that their data will be secure all the time from their own errors is the last thing anyone wants to do. Because hardware does fail eventually. It is not a question of if, but when. Wish I could tell my hard drive "Cancel the head crash." It is impossible to do that. By not putting up a "Cancel" button every action, Apple is naturally promoting (whether intentionally or not, which I can't say because of terms of use) a non-lazy user in terms of backing up. Because eventually a user will come to terms with their own propensity for making mistakes, and will need to learn how to backup their data to avoid mistakes from becoming costly.
People who desire to fiddle under the hood should be prepared to backup their data in case they make a mistake. By not providing a "Cancel" or "Undo" at every turn, Apple is no longer "holding your hand" at every step. Some users actually find it annoying to be held their hands, when they think they know better what they want.
Regarding the menubar, having a single consistant interface for all programs is reassuring, because you always know what program will be affected when you change things via the menubar. Numerous times in Windows, you'll find half a dozen menubars strewn all over the place with windows hiding other windows, and half the time you go and point at the top of a window, and expecting to make a change to one program, when in fact you are making a change to another program. By limiting changes to the active program by putting the menubar as one menubar for whichever application is active, Apple is actually reducing the potential for mistakes, or windows hiding each other. And for users who want more access to the windows, they can always use Exposé to navigate the windows, or the Dock to pick the application and choose a window out of the application.
It is a different principle of navigation.
http://developer.apple.com has plenty of resources for learning about Apple's Human Interface Guidelines.
I do not work for Apple. I just know what I observe makes more sense in the long run for many people. But obviously from the reponses to the thread, it is not all people.
- * Links to my pages may give me compensation.