The real story here is that if a company endorses SSM its reputation will suffer. Forbes, for instance, is trying to bury that finding with the headline "Higher Democrat Perception for LGBT brands" when in actuality brand support for companies perceiving to be pro-SSM has dropped among BOTH Republicans and Democrats:
"While overall Buzz scores for the index of brands have decreased among both groups, the decline is more significant among consumers who identify themselves as Republican."
Take a look at this chart for "brands which have publicly supported LGBT" filtered by Democrat and Republican consumers from January 1st to September 5th of this year. The brands measured are "Amazon.com, American Apparel, Apple, General Mills Brands, Google, Home Depot, J.C. Penney, Levi’s, Macy’s, Microsoft, Nabisco, Nike and Starbucks."
No matter how media outlets try to spin it the chart could not be more clear -- coming out for gay marriage hurts a corporation's brand:
Graph from BrandIndex.