1) Young founder with visions
2) Hacking culture (to the max)
3) Cool technology (Erlang, C++, Java, Hadoop, HBase)
Every time I saw a Facebook engineer giving a talk or writing a blog, the word "quality" (unit test, test, automation, manual, or whatever) and "documentation" are nowhere to be found.
It's not in the company's blood/gene when it comes to QA process. Maybe that's the reason why they're hiring super smart and super young individuals? to pull all-nighters fixing bugs and pray during the release day?
It'll be super hard to get better in QA because it's probably too late for them: too many hot-shot developers who aren't used to testing (automated or manual). They'll probably hire tons QA and automation engineers, but at the end of the day, their developers will "fix" bugs and throw it over the wall.
Some people might not like the way Google works (too much bureaucracy in terms of code quality), but they work really hard to make sure their engineers are responsible toward the code they produce. It's hard to have that kind of mentality embedded onto your engineers.