1) The nice bike employs 7075 alloy aluminum in its frame.
2) The crap bike doesn't.
3) The nice bike is better because it employs 7075 alloy aluminum in its frame!
Just that using aluminum for the frame is not the only indicator a bike is better.. so shallow in that regard.
Are we looking at the same link? The author goes into detail as to how the more expensive bike's frame is:
lighter
stiffer - built using shaped and butted tubing
less prone to corrosion
and then has a paragraph about different steel alloys and how some of the best bikes are made with the best steel alloys.