You wont see variant of modificator then as they are part of the 4.0.x versions.
The reason why you are not seeing the quantity boxes in the page you gave as an example is that what you are looking at is the products.tpl which doesnt allow product options out of the box, for that you would need to modify it yourself or pay for some to do it.
Out of the box x-cart only allows product options on the product.tpl (or more details as the page is comonnoly known) i.e
http://www.metzgerinc.com/xcart/customer/product.php?productid=16135&cat=249&page=1