Fully agree. 20-50ms for something like S3 is fantastic and proof that we live in the future. S3 is only slow when compared to interacting with redis or a FS layer powered by node (by about an order of magnitude). That's why I feel that complementing it with a self-managed FS can work well in certain settings. And interestingly enough, because S3 is so solid, you don't have to be so paranoid with your own FS layer, since S3 is there to bail you out in case of data loss.
Regarding S3 pricing, ~0.09 USD per downloaded GB could potentially become a significant bill (~90 USD per TB). I'm building a service that serves pictures and limiting the financial downside is very important for the economics of the business. More than the actual magnitude, the certainty that costs are a linear and predictable function of storage makes me sleep better.
An implicit point that I just realized by re-reading your comment: if you have a significant amount of data (let's say, > 100GB) a local FS is only cheaper if you're using instances or dedicated servers with large disks - and probably this is prohibitively expensive in AWS (EBS). I'm particularly considering Hetzner dedicated servers with large disks.