The number your comparison is missing, and one that happens to be crucial to both business and technical differences, is that you should be looking at tweet impressions, not tweets.
Also interesting is if impressions should be counting followers of the tweet author or only if the follower reads it.
Many users are following so many accounts that they can only read only a small subset of their timeline. I wonder if Twitter's apps and services also have to evolve substantially like Facebook's did to include more elaborate filtering and ranking options.
