That's not entirely true. Sure, you can implement VirtueMart (or something equivalent) with Joomla...but options exist for WP as well. WP-commerce, YAK and a few others. Or, you can go the 3rd party cart route and use WP for the static product content and kick over to UltraCart or something similar for processing.vouch for Joomla.. you can have great features with it like adding a cart and so on which u can't get with WP.