The jaggedness is in large part due to the resizing algorithms. I posted landscape+portrait modes of the same picture for a reason.
Damn I wish I'd know to post inline pictures. Anyways, you posted only the zoomed out photos because you're trying to prove a point. But the fact is that the "obvious" banding of gradients is caused mostly by the compression/resizing algorithm. Look at the landscape screenshot above. Yes there's a banding problem but it's not as big as you make it out to be.