For people nitpicking this scene, consider 2 things:
1) During the infamous scene, Greg Sestero is supposed to be on it. On this trailer, you can see him next to Rogen's character. This suggest that this version of the scene may not be the final scene we see on the movie.
Greg is in this scene, but he's not in this shot. Greg is in the following shot, when he's sitting in the corner on the chair and Tommy comes over and sits down...but that's a completely different shot that very well could have been filmed on a different day (and probably was, considering the "I did naaht" shot took 3 hours to do).
Unless there are details I'm missing from the book, that's how it plays out to me.