While the band broke up decades ago, and half of them are now dead, the remaining Beatles weren't just going to sit by and watch somebody make a game based on their career. So they helped.
Harmonix's Chris Foster, who is serving as lead designer on The Beatles: Rock Band, elaborates:
The shareholders, as we call them — Paul and Ringo, Olivia and Yoko — were really creative partners throughout the project. They were involved in picking and approving the song list, the venues we went into. With the dreamscapes, they saw storyboards of all of the material, and gave feedback on whether or not they felt like those interpretations supported the songs in the way they wanted.
They looked over all the characters, the animations... they really kept us honest on whether we were capturing the spirit of the band as they were performing, which was a huge challenge for us... At every milestone they improved it. I think Sir Paul McCartney heckled our project lead's bass-playing when he saw one of the game demos. So yeah, they were involved.
You know, Yoko Ono was wheeled out at Microsoft's E3 press conference, and name-dropped here as well. I'd think her contributions would be a detriment to a game based on, you know. The Beatles.
You Say You Want a Revolution: Chris Foster on The Beatles: Rock Band [Crispy Gamer, via Go Nintendo]