UL98 vs. UL508 disconnects

I was on ABB's site and a ul98 disconnect is over double the price of a ul508 disconnect (non fusible enclosed disc switch)for the same amp rating, anyone know why that is? If I can use 2 of the ul508 disconnects for a motor and a heater why use a ul98?

thanks

Just a swag here, but is one a load break switch?

Decent explanation here:

http://www.ecpzone.com/publication/article.jsp?pubId=1&id=3568&pageNum=1



-Eric