The groom's cake is actually a Southern tradition, I'm not even really sure how it started or why, but you see them a lot there (in fact, if you're a fan of the movie Steel Magnolias, the horrible armadillo cake at the wedding in that film was the groom's cake.) I think it was to make sure there would be enough cake for all, back before it was possible to make the enormous tiered things we have now? So maybe the groom's family would help contribute in that way (keep in mind, there didn't used to be the huge amounts of food you find at wedding receptions these days, either..cake was pretty much it.)
Anyway, in England wedding cake is traditionally fruitcake. Yuck. So we compromised a bit by having chocolate. We thought that way, not only would we have the Brits represented, but people who prefer chocolate cake can have some without the wedding cake being chocolate (especially important because the bride at our wedding, me, doesn't like chocolate cake
).
People really liked it, too! It was nice to have two different ones to offer, and since my Mom made it with a regular mix and food-colored frosting, it was nice and cheap.