Either that or I'm dense and I'm not trying to be.
I think you are focusing on the term "spellcasting" and saying that just because something (a feat or whatever) refers to "bard spells" that it does not imply "spellcasting." That doesn't make any sense at all to me, but it is what I infer from your comments. I'm saying that anything that says bard spells or refers to a bard casting spells obviously applies to bards whenever they cast spells. Thus, all of the above apply to bards, and thus to assassins (if you follow #1 -- which I do not, btw).