Ok, some confusion on my part.
I looked here
http://elementscommunity.org/forum/index.php/topic,11691.0.htmland read
"Immortal/Protected The creature or permanent can not be targeted. It is also not affected by spells that affect all creatures (e.g. Firestorm), or abilities that affect the field (Flooding). An immortal creature can still be affected by shields."
So, either you are wrong or the info on game mechanics hasn't been updated yet. I'm guessing teh 2nd one.
I was doing some card creation and made a card which turned all creatures into vanilla creatures and the question came up if it would work on immortals or not. And according to your understanding of the rules it would work if the card was a permanent and not a spell. Correct?