[Plugin: Affiliates WooCommerce Integration Light] Why does this require another affiliate plugin to

The Affiliate plugin is just a stand-along affiliate plugin. Then they’ve created various plugins like this one, to connect it’s functionality to different ecommerce solutions: WooCommerce (this one), Jigoshop, WP-eCommerce, etc. So rather than having different versions of the main plugin for each, they just have these little “bridge” plugins to connect to whichever store plugin you’re using.