I've noticed that too about the shoulder straps...don't use them all the time but something about the way they sit make the bag seem lighter.The Olivia is heavy with the suede lining, but I find that with the shoulder straps, it's so comfortable - somehow the way it's constructed makes them never slip off and make the bag feel infinitely lighter.
The woven arm handles sometimes seem a little weak like they won't be able to support the weight of the bag - and I've heard people complain that their handles broke or unraveled...