Comment 27 for bug 1347305

The point was to make things look nicer and to pave the way to the future changes to the compose ui. Things will eventually be entered in one field, with multiple addresses per line, improved contact support, drag and drop address movement and other cool things. However, In an effort to accomplish this, we want to get away from classical and dated ui.

That's the reason, hope it clears things up a little.