IANAL and all, but this is almost certainly not the case. If anything, it's rather to make it clear to people that they are on their own if they put in a random kernel. You know, so that you can't sue Nokia if you get 3rd degree burns from mismanaging the battery or have your emergency calls fail because you did something funky to the kernel or sorts. To assume that this is some elaborate schema to avoid (otherwise perfectly reasonable) replacements sounds to me borderline paranoid, but hey, to each his own.