Shopialize primarily focuses on sharing "post-shopping" updates quickly and frequently like micro-blogging way. Other social shopping networks primarily focus on "pre-shopping social bookmarking" and "wishlist creation" aspects. It doesn't tell if your friends or community members are really buying those items or just recommending it.
Also, I'm not trying to build another social shopping network. I'm looking more towards Twitter+FriendFeed integration. Twitter may-not provide better shopping related feature-set. Similarly, FriendFeed may not add all social-shopping services like Kaboodle, ThisNext, Kirtsy, etc., which I'm planning to add soon.
These are primary reasons. Hope this answers your question.