Exactly, and my point is that currently my ISP assigns IPv4 addresses dynamically, so I'll get a different one every time I turn on my ADSL modem. I think this is quite common, and as a consequence IPv4 addresses are not a reliable way of identifying a home computer. If every home connection is assigned a static IPv6 prefix, that becomes a reliable identifier. Then you can credibly say "This comment on my blog is from the same computer as this Wikipedia edit from last month!", something you currently cannot say for home computers in general (while work computers are much more likely to have static IPv4 addresses and in that case IPv6 doesn't make it worse).
As I understand it, the privacy extensions in IPv6 were designed to solve another, bigger privacy concern that was totally absent from IPv4: if the second part of the IP address is based on the MAC address, then smartphones and laptops can be traced globally, no matter where they connect to the network (home, hotel room, 3G...)
