It occurred to me that Ignatios Souvatzis wrote in gmane.os.netbsd.ports.i386:
> This should not be necessary, unless you pretend to have IPv6 connectivity
> (that is, a route to the destination) but no packets pass through it.

I know that there is (or more precise, I know that there has been) software
in pkgsrc which isn't behaving like it should in this matter. One example
is dillo. If you try to visit a website which has an AAAA record, and if your
kernel supports IPv6, it will try to connect there via IPv6. If this fails
because of a 'no route to host', it will leave it at that, and it won't 
try ipv4.