The fashion editor from Golf Digest has hated white belts for years. I'd say it's been at least three years I've been reading "articles" with him criticizing white belts and how awful they look. But every year you see just as many white belts. So I think that statement has more to do with his personal preference than it does any style changes.
With that being said, I don't think white belts are out as much as colored belts are becoming more popular. You could just as easily say black belts are out because guys are wearing them less. When in reality, it's simply because they are taking advantage of more readily available options out there. I still have a couple white belts and I won't hesitate to wear them. But I will admit they will probably get worn less as I add more accent colors to my belts.