Maybe the book is popular enough that I can easily find 5 people to share the story with already. If we are all ready for the end chapter they are all there, ready and waiting to accept the invite, we don't invite people who like to constantly re-read the parts about standing in fire, and everybody already knows to loot the corehounds (oops.. spoiler).

"A mum in my street with exactly the same access to information as me has two horrendously overweight and unhealthy kids (seriously, adult weight at 13, thats serious, and they started off thin)."

Sounds like a genetic/dietary problem to me. Don't blame the games, maybe if they had a healthier diet they would feel like moving around a bit.