expopower: Yeah, I remember some sites featuring bundles like these in the past, guess they're here to stay! Honestly, I was just a bit surprised that there's a market for games centred around extremely...intimate familial relations. I guess I've not spent enough time on the internet. >_<
Uhm, there's a market for everything but it's still a ninche and that is why they're charging $10 instead of the usual $1~$5. If we think about it, it's the same for the Steam cards, normally they cost 0.05~0.10€ but if it's from a visual novel (with anime girls, bit tits, etc) it's 0.30€~0.50€.
Hell, if you're quick enough you can profit from those VN bundles by selling the cards (the money would be stuck on Steam though).