Are (were) any of these essential for Facebook's success? I doubt it. They are by-products of Facebook hiring talented people after they already had a leading product.
> one must assume that these projects are, in fact, essential to the continued success of the product.
In the same way that Google Reader, Google Wave, Google Base and dozens of other products were essential to continued success of Google for a while (before they were discontinued), just because they were developed at Google?
Yeah. OP has never worked near any of these companies. Writing some basic linear algebra routines in python doesn't mean you're doing the same work that Google has to.