2. Menus are a useful way to discover the main features of a program. That is, the user can be in 'browsing' mode, not just 'searching' mode.
This wouldn’t really work if every app had to implement this feature on its own, probably in different places and with slightly different behavior. Even if the behavior were consistent you still could never be sure whether you can search in the first place, that uncertainty is in my experience a good way to make sure a feature will never get used.
This seems like a great OS level feature.