I always wondered about these, as the seatpost isnt able to drop any lower than the top tube due to the shock, does the extended seattube flex much? later models obviously have a reinforcing tube from the extended seattube to the top tube.
It wasn't the later ones that had the extra bracing, it depended on the material. Steel frames don't have it, but the aluminium and Ti frames do.
And yes the steel frames are heavy they are made from 4130. My old Intrepid frame was over 7lb. and was dubbed he "Black Anchor" because of its' weight. When we had to get it on the car roof mounted bike carrier, it was almost a 2 person job!