Seeing how Apple acquires businesses, they mostly concentrate in those that will add future technologies (i.e.: Fingerworks with Multi Touch) or potential future technologies (PA Semi, new ARM chips for future iPhones?) or software that create future content (Shake) by Content makers (TV or movie studios)
Twitter is in essence messaging, and Apple would only need to build hooks in iChat and other apps to take advantage of it's popularity without having to spend $700 million. By itself it only generates content (when breaking news happen), or idle chatter (most of the other time).
NO, it would not make sense for Apple to buy Twitter as it doesn't add anything to the existing product line.
Buying EA, also, doesn't make sense. EA works with all platforms and Apple would most likely consider a game company that would be exclusive to it.