I worried about the width issue also with the planet bike fenders on my 26". My Schwalbe tires are 1.6". They look fine and the extra coverage does not hurt a thing. I agonized about different types of fenders, the PBs are already put together and pretty easy to install. As others have said, if you decide to run a wider tire...
I went ahead and cut all my struts down, since I was pretty sure that I wouldn't be going with a bigger tire. PB does sell spare parts for the fender, they got ya covered if you cut them and later decide to upsize tires.