Thank you for your answer gordontaylor, but if could explain to me something...
If you leave a comment on a product, that review it does not appear in the source of the page ( in the HTML language ). So... how could a Google Spider crawl that comment if it doesn't exist ? A robot doesn't crawl what users see on your website, but what he can reads...That's my opinion and i don't consider myself a SEO EXPERT.
The reviews on AbanteCart can be moderated, so any mark of spam and unnecessary links can be removed, there vizibility are very important from my point of view because i need to set rich snippets for my products and i need that information to. Beside that, a text from a review means fresh content for that page, so is good for SEO.