That is the case for most ISPs, even the ones participating in SixXS. As there is no root IPv6 glue anyway, this does not matter. Next to the fact that you have IPv4 simply because of the fact that you are taking a tunnel, which goes over IPv4; thus you can resolve any issue with this by simply NATting IPv4 and doing native (well tunneled, but not translated :) IPv6. Having a local IPv4/IPv6 connected resolver is anyways a good thing. I can't claim that you are unable to use Google anymore (actually, they don't have IPv6 records for their nameservers, nor their load-balancer either, thus you would not be able to reach them IPv6 only), but there are a lot of resources on the Internet you could not reach anymore; now the moment you include an IPv6/IPv4 proxy, that thing can do the resolving also for you, thus problem resolved again.