Back in the 90s, watching Buffy, I wondered just why the heck every single character was an only child.

Ohhhh, good point. It's true, Simon and River are the first siblings in the Jossverse who get introduced as siblings at the start of the show, neither of which gets killed off, and whose relationship is important to their show. And lo and behold, what happens in fanfic?

And, of course, the fact that they enjoy taunting the fans with lines about how "there's a dark secret in the Petrelli family" just convinces me more that they love messing with us.

I think that was settled for me as soon as I saw what kind of promo pictures they released for Fallout. I mean, come on (http://www.sparklies.org/gallery/albums/Heroes/Promo_photos/ep01x11%20-%20Fallout/Heroes_Ep1x11_Fallout_05.jpg)!