I know nothing about real drumming. Nothing. And the first thing you learn about drumming in Rock Band is the most obvious: it's not as easy as it looks.
First, you have to learn to keep rhythm. And since you are drumming - you can't follow everybody else's rhythm. If you are a Guitar Hero player, you get this immediately. Everything feels disjointed at first if you're too used to the notes you hit corresponding with the lead guitar.
After a while, you can used to it, and all is fine with the world. Then you move to the higher difficulty songs, and you realise how much of a challenge it is to keep your bass pedal leg in sync with the beat. At some point you get it, and repeating patterns with both your hands and legs is no problem.
Then, after all that work of getting your legs to sync with your hands, you find that when you up the difficulty, you actually need to work out what is called 'limb independence'. This means the ability to hit any of the drums at any time. So you know that clever trick of syncing your right leg to your right hand that you learned earlier? Now it's time to unlearn it - while stepping on the bass pedal really really often.
Now, if you're like most people, when you start, your leg is likely in the wrong position or posture, and as stupid as it sounds after you learn otherwise, you keep your foot raised in anticipation of the next note, instead of just resting it after you've hit the note (and raising it when needed). Needless to say, most people get their legs tired really quick.
But if you're like me, then this stage is quite important - since this allows you to learn the first level of timing. Then, comes the second level of timing - lifting up your foot and stepping down in time. If you're lazy (like me), you'll figure it out soon enough that resting your foot is an optimal strategy.
After all that, then pretending to playing drums in Rock Band is a breeze.. until you see syncopated bass hits.
(Although that's about the point when you are about to enter the region where Rock Band drumming skill = some amount of actual drumming skill - minus familiarity with an actual drum set and a hi-hat pedal and of course any semblance of ability to write a drum part. Maybe.)