The problem I see is the mentioned sites in the links are all famous designers. They are heavy on images with little text to help with
SEO and the ones where I looked at the code had poor on site
seo. But these companies can afford to do that as people will search for them by name anyway and they have tons of good inbound links. They are also mostly are for artistic types of products such as designer handbags.
It does make me curious how versitle the wordpress ecommerse plugin is, as they are correct, most carts look pretty similar. It might be worth struggling through some of problems with the wp one if the presentation is more versatile.