The idea, of course, is that you can look for the companies you buy from on the list, and see how they stack up in terms of providing benefits to their GLBT employees. Then you can make better purchasing decisions.
I was surprised to learn that most of the companies I do business with are pretty gay-friendly. The only exception to that was Food4Less, and I stopped shopping there sometime last year when I found out they are a division of Kroger (which has a score of 35/100). I was also rather surprised to learn that Circuit City comes in at a mere 55/100, whereas Best Buy gets full credit.