Thanks a lot for chiming in!
Interesting, I think this is very DIFFERENT from the other texts. Most indicate clearly that "You don’t have to subtract your scores in other Supernatural Abilities from your advancement total when you are learning a Favored Ability", but I didn't get that "you don’t have to subtract your scores in Favored Abilities from your advancement total when you are learning other Supernatural Abilities from the same realm" except for the Infernal.
HoH:S explicitly says that "The Source Qualities to learn Favored Abilities are still penalized by scores in other Supernatural Abilities, and scores in Favored Abilities penalize the Source Quality to learn other Supernatural Abilities", which seems to contradict the above.
The Faeries text is most vague, as it talks about "the others" and it isn't clear if this refers to other Favored Abilities or all Supernatural Abilities.
Oh, nice to know. I didn't notice that.
Yeah, I don't remember seeing a note on that, but there is a note saying getting two supernatural abiltiies from two different realms is generally discouraged and all-out forbidden for Infernal & Divine, so I reckon this applies to traditions too.