Off course they are different, Amazon's shopping cart was developed by themselves with Professional web developers spending hours on it and doing upgrades etc..
Although I'm sure you could restructure a Shopping cart script to look more like Amazon, I don't think you are going to find one that exactly mimics Amazon.
The look of the Shopping cart can be modified, using CSS and HTML, but you'd need to know a bit about both to get into the shopping cart pages and modify them.
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Ignorance is not necessarily Bliss, case in point:
Unknown has caused an Unknown Error on Unknown and must be shutdown to prevent damage to Unknown.