In biochemistry, chemical reactions are helped along by catalyst. It takes a certain amount of activation energy for a chemical reaction to occur, and if there is not enough activation energy, the reactor halts and never happens.
The activation energy to author an E-mail is often higher for the user than a short tweet in Twitter, and thus a user, once acclimatized to the Tweet-space, will find that the profile-to-interaction ratio is higher than one's E-mail list. The reduction of time and space that exists in the world of Twitter acts as a catalyst for greater communication. Greater communication leads to smoother and more enjoyable conversations in real time and space, as Twitter members are used to conversing quickly about a number of things.