True I think it did say that. Why the hell would that be though. And if so, that'd be enough to prove Loghain wrong early on.
I don't know, but my best guess is there are more genlocks and hurlocks because the darkspawn come into contact mostly with dwarves and humans. Dwarves because they live underground and fight the darkspawn constantly. Humans probably because they're the most numerous of the surface races, and so have the sheer numbers for the darkspawn to corrupt.
The Qunari are not as numerous, and mostly live far north and weast. Since they're so few, so far out of the way, and so physically big, tall, and imposing, they're probably considered too much of a hassle to try to fight, capture, and turn for most mindless darkspawn raid parties. During a Blight, the darkspawn have the eerily competent Archdemon telling them what to do, so the Archdemon probably tells them "Go capture those giants and taint them so we'll have some muscle in our ranks. Yes, I know they're bigger than you and they pack a wallop. Listen to my strategy: this is how you take them down."
As for elves? I don't know. The Dalish are very adept survivors in the woods, and elves in human societies are mostly servants and laborers who remain in the city alienages, or hang back cleaning the trade caravans, polishing armor in army camps, and warming seats while their human masters do important things. Maybe their line of work doesn't leave them vulnerable to encountering darkspawn, which in turn don't seek them out until an intelligent mind tells them to hunt them down during a Blight.