The difference, as the law as currently pratised seems to work, is the difference between stating a view and broadcasting it. A tweet is publicly available (even if only a select view will ever care to see it) so is assumed to be a broadcast (in the same way a radio statsion listened to by just four people and their dogs would).

Sometimes tweets are taken as incitement to others to take the view (or take actino on the view). This is often over-zealous though not always wrong: take ol' wangy-eye of the BNP and his suggestion in a tweet that peopel picket a gay couple's home for instance.