It's because you could have sex with 13-year olds. Most consider the cutoff age(initially the settings may have influence, like if it's set in the middle ages where 13 is close to being 18, etc.) at about 15. Some may say 14.
But 13... that, yeah, I can see and get the point where he's coming from.
The reason why FATAL is different is that it's extremely notable and simply gets a stubbed page to note that it had influence on the Tabletop RPG community. That, and nobody read the Rulebook, so perhaps we don't know if it really is pedophile-pandering, or some misread/misinformation. Thankfully, I'm looking for one and can tell you if it really does give that option.