Is it harder to make a successful color landscape photograph?......Hmmmmmm. No. I think it depends on which you practice at more. I also think people feel color is more difficult than BW because they do not understand it. To me they are about the same in difficulty. In color you have to think about the color relationships in the scene. In BW you have to worry about the tonal relationships. I think there are the same number of factors to consider they just take a different mindset.
Plus, people like making what they do sound more complicated than other things, so they sound like they are working harder.