That's not entirely true now but has been in the past. They've actually tied their fates to both AWS and GCE in different parts of their infrastructure. The obvious example of this is the one or two global outages they've had due to misconfiguration in GCE this year.

I know their video encoding platform is heavily tied to AWS because the teams that built it optimized for cost (which for them makes a certain amount of sense) and they massively parallelize the encoding work. I talked to some of their engineers at re:Invent last year and it was kind of interesting. They aren't using a lot of AWS-specific stuff though, just AWS EC2 reserved instances.

I don't think that just because they're Netflix that everything they're doing is correct. This can't possibly be true.