Those reviews are a bit thin on the positioning of Magento and the other carts (it is hard to say they are unbiased either as they are Magento Enterprise designers/developers)..
In summary my answer based on serious experience of the main AJAX-based open source carts since 2009 is that Magento is for you if you are a mid to large corporation with a dedicated programming team or a budget to pay for support. It has a lot of buzz over the last couple of years and a large community of developers (although you will find a very steep learning curve -- it is not for the lone store owner).
If you are a small to mid size online store I continue to recommend PrestaShop. Although now that Virtuemart V2 is out there is finally something to look at in alternative with that cart running on the Joomla CMS.
What you may ask, about OpenCart? Well unfortunately it is difficult to recommend Opencart despite its clean looking design and healthy paid for extensions store where you can usually buy the features you need.
Please bear with this old demon. I will explain a bit more so that potential Opencart users can research and make their own minds up.