actually, it's not true, as the Silmarilion wasn't exactly tolkien's work (well, tolkien it was, but Tolkien son actually). It's just a damn lot of notes written on a corner of a page, lose sheets of papers, letters to students, stuff like that, that his son gathered and rework to pu ti together. That's why it has some inconstancies or even incoherences, Tolkien was often contradicting himself in two texts, and according to his son, the silmarillion was quite some piece of work to put together.
Funny you think Bombadil is "ridiculously powerful" btw, when I read about those sci-fi species from your books, that can create universes and stuff. That is ridiculously powerful, not the fact that a guy can resist to the attraction of a magic ring. Actually, you want to know my theory of why he didn't feel anything? I think Bombadil is... her... warning, that will sound dumb, but anyway:
I think he's perfectly pure, not a single bad part in his heart, he's not greedy, not agressive, he's fair. The One Ring emphasizes on people's defaults to seize control over them, as did the lesser rings. The ring just can't use anything like that on Tom, and so the fellow is not threatened at all by it.