Comment by aidos

I don't think I explained that very clearly.

What you see as zone A is not what I see as zone A (maybe). When you sign up for an account, AWS assigns your zone A to one of the 3 available zones:

    zone X (real) : your A (virtual) : my C (virtual)
    zone Y (real) : your B (virtual) : my B (virtual)
    zone Z (real) : your C (virtual) : my A (virtual)

That's why people see different outage characteristics between the zones.

Edit: one of the few articles (other than HN comments) that explains it https://alestic.com/2009/07/ec2-availability-zones/