Joomla vs Magento

Joomla is a free and open source content management system (CMS) for publishing content on the World Wide Web and intranets and a model–view–controller (MVC) Web application framework that can also be used independently.
The most flexible enterprise-class eCommerce platform to power your business. It's got the enterprise-class features and the flexibility you need to create an eCommerce solution tailored to your unique needs. And to help you drive more traffic to your store, convert browsers into buyers and boost online revenue.
Face to face in the news:

2013 - Magento improves interface performance to compete with Joomla

The newest version of Magento Enterprise Edition– version 1.13 – is now available. The developers optimized the indexing process to enable significantly faster indexing with limited to no impact to the customer's shopping experience. This will make it easier for you to add and update products more frequently while ensuring your URLs, promotions, navigational menus and product search tools are always completely up to date, while never slowing down the performance of your online store. The full page caching capabilities enable even greater performance by invalidating only relevant pages making it easier to cache content without affecting site performance for your customers. Improved caching performance also drastically reduces server load enabling your to store to support even larger traffic volumes while conducting back end operations. Thus Magento becomes more fast if compared vs Joomla