I wonder who the first rock act to debut with an album of all originals? That surely is a groundbreaking event.
Only groundbreaking if it sells. (The first off the block might have disappeared in a sea of disinterest.)
I think there is something about the familiarity of a well-known song. I have to say, I was absolutely delighted when I first heard the Beatles do "Please Mr. Postman", because I was so familiar with the girl-group version. I just sat there grinning:
boys are doing this! So the Beatles didn't have to win me over to this new song (as in, "Please learn to like 'I Saw Her Standing There' enough to buy our album") because I already knew the song, and I thought the Beatles singing it was really cool.
So perhaps after they'd established an audience and marketing was no longer an issue, they could feel more confident that their albums would sell even if they featured "only" Beatles compositions.
Coo discussion, everyone!