I'm also amazed by this, and also the way phrases and titles of Beatles songs have become everyday speech (check out how many news stories use variants on 'Ticket To Ride', 'Eight Days A Week' or 'A Hard Day's Night' for example).
For a song like 'Give Peace A Chance' or 'All You Need Is Love', Lennon recognised the importance of simplicity (probably the wrong word) and the various detractors of Lennon/The Beatles will jump on this straight away not acknowledging that songs like these HAVE to be simplistic in order to cross political boundaries and difference of language to become universal.