The # of watchers is a good early indication of the liklihood of an auction item selling at a favorable price, because it shows interest. For a fixed price item, it means nothing but curiosity. If the price is fixed, and a person wanted to buy it, why watch? It's not like the price is going to change. 99.9% of watchers of a fixed price item just want to see if it sells. or flames out.

Auction items get watchers that are curious or looking to buy, and the more there are, the better the odds of buyers competing.

Fixed price items either sell or they don't. It's not like the watchers are waiting to see if the price stays low.