I think it's simply wildcard SSL getting in the way, if you put a . in the bucket name, the DNS record becomes a.b.c.s3-xxxx.amazonaws.com The wildcard SSL cer

I think it's simply wildcard SSL getting in the way, if you put a . in the bucket name, the DNS record becomes a.b.c.s3-xxxx.amazonaws.com The wildcard SSL certificate they use only matches the c.s3-xxxx.amazonaws.com part of the sub domain