1) ipv6.google.com only has a AAAA record, no A so IPv4 can't connect to it (that and its on IPv6 (hint: neither stack are compatible))
2) this is an IPv6 enabled web frontend for their site, however they are NOT indexing IPv6 websites
3) the google URL you link to, while mentioning ipv6.google.com, is actually about getting your nameservers whitelisted so you can access www/mail/news/images/video.google.com (etc..) over IPv6 using their standard dns scheme and not have to worry about using the IPv6 only hostname.
If you want to see a site that is already indexing for IPv6 enabled websites based on submissions, try sixy.ch. Warning: you need IPv6 connectivity to view IPv6 only sites, dual-stack however will obviously work for IPv4 only websurfers.