No.
Less than 14% of the photos on MadcowModels contain nudity. If photographers were in it for nudity, wouldn't that number be *significantly* higher? Of course it would. Its simply down to who modelling is targetted at, and shows such as the "next top model" series feature female models only. Magazines feature a lot more female models than male models, most media probably does, and so the whole modelling world is thrust in front of females a lot more than males, therefore its a lot more natural for females to want to try modelling than it is for males.
James