Yev from Backblaze here -> we actually have datacenters in California and Arizona so they aren't too close together! That said, we're also working on multi-region support so that you could move data between regions (no ETA on that yet). Hoping to get more datacenters online in the coming year!
But you're correct - we do recommend diversification, having data in multiple locations is always a best practice, and if you can have it in different vedors, all the better!
We're still working on the spec so hard to say, though even if we did make you pay for it you could store it in 4 regions before hitting S3 pricing :) That said, we try to be fair in most things we do.
Meh, for true redundancy you need separate vendors with different hardware and software infrastructure. Erasure coding and bitrot guard hit the 5 9s I need.
But you're correct - we do recommend diversification, having data in multiple locations is always a best practice, and if you can have it in different vedors, all the better!