I'm curious what differences there are between the services that would make Facebook pick Ustream over Justin.tv. Was it something in function? Aesthetic? (Ustream's front page admittedly looks a lot sexier.)
Facebook definitely has more stature, but I'd say the opposite of your comment holds true. The larger companies are scrutinized more and have a higher standard of quality to uphold. Larger companies choose the best possible and the most professional partners. If things go wrong, the bigger company suffers more when it comes to "brand".