I also don't know if it is spelled out, but im with you, the BOD+WIL drain is probably just used for Adept Powers Adrenaline Boost and Attribute Boost.
Although both say in the last paragraph resist as normal - suppose it means "resist as Adepts do normal for usage of Powers"?
So probably a better wording for the 2nd Adepts Paragraph would be:
> Adepts [and Mystic Adepts?] have to resist drain from some Adept Powers with Body + Willpower.
instead of
> Adepts sometimes have to resist drain, which they do with Body + Willpower.