I'm a Facebook engineer and I definitely feel that Facebook is willing to take those 5% chances. Heck, one of Facebook's mottos is "Be Bold".
As an intern, I started a project on my second day at a Hackathon that had absolutely nothing to do with my assigned team. I ended up devoting the second half of my internship to that project and by the end of the year I took an offer as a full-time engineer at Facebook, still working on that same project that I had kicked off on my second day.
I'm not here to say Facebook is way better than Google; I think they're both amazing companies. But the idea that Facebook isn't willing to take crazy chances definitely contradicts my experience at the company.