--- Collection.php	(revision 2102)
+++ Collection.php	(working copy)
@@ -553,7 +553,11 @@
                 ->from($this->getTable('core/url_rewrite'), array('product_id', 'request_path'))
                 ->where('store_id=?', Mage::app()->getStore()->getId())
                 ->where('is_system=?', 1)
-                ->where('category_id=? OR category_id is NULL', $this->_urlRewriteCategory)
+//                excluding this clause to facilitate one URL per product, and one that includes the category
+//                if a product has multiple categories, the first one (by category_id) will be used
+//                in most cases you'll probably only have one category because you only want one page per product for SEO reasons
+//                for maximum link juice, no possibility of duplicate content, and a less confusing store
+//                ->where('category_id=? OR category_id is NULL', $this->_urlRewriteCategory)
                 ->where('product_id IN(?)', $productIds)
                 ->order('category_id DESC'); // more priority is data with category id
             $urlRewrites = array();