Careful now ...
If there is to be different rules for tweets (micro publishing), then how will be know who has different rules to follow. This is dangerous as this situation shouts accreditation for the press (one set of rules for professional publishers), and another set of rules for amateur publishers. Who awards accreditation? The state?
I think we need a sense of proportion here and resist the temptation to separate the press from the rest of us - that is a much greater evil than the amateur mistakes by a few with very little reach. We need fewer laws and more discretion by the police, judges etc.
Ms Bercow, being the Speaker of the House of Commons wife, living in the House of Commons, and constantly in the press, should have known better though.