True. Maybe a half-dozen additional races, but with a deeper culture to draw on and different factions within those races.
Why do we need more races than presented in the book? I personally don't want the official setting to turn into some D&D clone. IMO, it has just the right amount of sentient races to feel like fantasy, yet still retain its own identity in the glut of published fantasy settings.
I understand your reservations about adding more races to the setting. I just feel that it could do with a few more sentient races to add some variation. I certainly don't want to see 5 or 6 additional books of races like D&D/Pathfinder, but a half-dozen well developed species that could either be antagonists or possible allies as the adventurers explore Ravenlands or other areas would, in my opinion, be beneficial.
I like what I see of the setting so far, it's not that I don't like the races presented, but I just feel a few more would be good too.