During the early LZ years, Robert Plant was simply astonishing. His vocal range was unbelievable and as Otto put so well, Robert was still very young and artistically so mature, it's really amazing.
But his voice changed... and I really can't see any problem in it. He learned to use his voice in wonderful ways, he was and still is a fantastic singer, in my opinion, the best ever.
And I really like his voice in ITTOD too. Some people say that it isn't his best, I just can't agree. I really love his singing on this album as well on his first two solo works. I also think that now he sounds even better than he did as he was in his mid forties. His singing in Dreamland and Mighty Rearranger is awesome, he sounds like never before: more mature, more conciuos of his vocal power, he knows very well how to use his best now. And though I have always said that I'm not a big Raising Sand fan, I have to admit that his singing on this album is even better than much of his singing as he was younger.
It's amazing how Plant still can surprise us.