Yes i would agree with you, even my online shops do not use the weight mod.
I would suspect the weight is more for a shop that does not use the weight for shipping calculation but maybe for a product, for example selling fitness equipment (weights).
Or maybe a product that is the same but different weights for different prices, for example fruit, or sweets.
I just thought i would post this as well as the shop_by_price.tpl
I am working on shop_by_size.tpl where in product options you have the size of the dress, but having a few problems with this one. You can see
http://forum.x-cart.com/showthread.php?t=52804 for more info.