Yes, eventually. According to the FAQ at
http://www.worldipv6launch.org/faq/ , both will work now and also for the foreseeable future. Years from now, websites will begin offering IPv6 only, but for now those offering IPv6 will also offer IPv4 in parallel.
That was my question as well. Working in a mixed OS environment, I'm familiar with NIC settings that Windows XP sp3 lacks IPv6. My conjecture is that once MS stops supporting XP (is that like 2016?), then sites would begin turning off IPv4. It is not determined as yet when this will happen, but it will most likely be once a majority of consumers can manage without it.
Executive summary: Not now. Sometime in the future, surely.
