Here's a bit to back it up:
Until Proven Guilty, several books into the war against the Vampires, Harry didn't know that some White Court vampires feed on Fear - or anything other than Lust. Which seems to imply that no one talking to Harry (during the time that Harry is helping to train the Baby Wardens) mentioned anything about how some White Court feed on anything except lust.
Which makes me think it's either rare for one of them to feed on anything except lust - implying that fear and despair might be acquired tastes.
As for multiple emotions - I could be wrong here (that book isn't handy) but in White Night, didn't Madrigal feed on lust (or did another vampire trigger Molly's orgasmic flashback)? Which does open the door to beings feeding on more than one emotion.
Richard
Harry is an eminently fallible narrator.
The list of 'facts' he's gotten wrong through the books truly would be impressive.
With regards to this one, Raith is the most prominent of the three major Houses of the White Court, and though the 'major houses' bit implies the existence of other houses, not even the WC characters have mentioned them in any way, nor were they seemingly present during the ghoul incursion incident (or at least not recognized as present by our narrator).
Being the most prominent House, and moreover the one most active locally, Raith draws more attention and gives Harry less excuse to be ignorant of their workings, not that the comparative absence of excuses prevents Harry from being largely ignorant anyway until his brother lets him in on family secrets.