Both Microsoft and Apple's www sites use Akamai's CDN, via a cname to a CNAME to something in akamaiedge.net, which support ipv6. The apex record of a domain (that is, the root record, microsoft.com or apple.com) cannot be a CNAME, it can only have an A, NS, MX or TXT record. A records make dynamic infrastructure hard, because they require API coordination between your DNS provider and your CDN. So Microsoft and apple host their own apex domain records via A records to static IPs in their own IP blocks, and have these servers issue a permanent http redirect to www.
