Conversion the term is relative actually. It does not always means that getting sales for your product or your affiliate products, some times it may be just getting sign ups or just generating revenue. So, people must focus on the sole purpose of their investments in order to get good ROI.
I was thinking just the same thing. Some of our clients started an ecommerce store they also started promoting affiliate products which are far less valued (not to mention low priced) from their original product. At first they got many sales for the affiliate product so they focused on them instead of their own product. As the result the site fall apart as the affiliate products soon lost their value and the sales of their own product couldn't meet the ROI.
Getting sales and generating revenue is conversion if you ask me.
One way to increase your conversion rate is by having more landing pages.