It appears apple.com and microsoft.com are failing this for the same reason; apple.com does not have an AAAA record. www.apple.com does. If you visit apple.com over ipv4 or dualstack, apple.com will answer and redirect you to www.apple.com, which is dual-stacked. But if you visit using only ipv6, apple.com is not found, so you're never redirected to the capable www.apple.com.
(ditto s/apple/microsoft/ - I just picked the example quickest to type)
(ditto s/apple/microsoft/ - I just picked the example quickest to type)