I'm a bit naive when it comes to infrastructure, since I've never managed it myself. I've always been in companies with dedicated infrastructure :).

Why does Netflix outsource to AWS?

The gripes I've had with dedicated infrastructure team is their knowledge/experience can be hit or miss. My current company is about saving money, so sometimes there's junior guys on there. Or there's guys who need to handle 20 different products, they're good at 10..but suck at the other 10. I personally don't believe they have best practices (but I'm not an infrastructure expert), because downtime happens.