Just because The Beatles are in Rock Band, that doesn't mean every single Beatles album will be in Rock Band as downloadable content. Why, you ask, well here is why.
Harmonix's John Drake tells game site BBPS: "Every time we do one song, it's not like Rock Band where we wait for the masters to come in and just author them... It's like, send people to Abbey Road, use the original tape, separate them out... it costs thousands of dollars. We're waiting to see how things sell. We're waiting to see how the albums do. If they sell well, we'll have a lot more content."
And if they don't, we won't. And if it rains, bring an umbrella. And if you are feeling hungry, eat something. Oh, if you are tired, then perhaps sleep, and if everybody thinks that you're lazy, don't mind them. They crazy.