As far as I know, these middlemen are deployed by the respective ISPs and are not a core function of ipv6. I've had the 6to4 (or AFTR, I'm still not sure which) fail on my ISP and could only reach ipv6 enabled hosts, sometimes for hours.
Not strictly required for the ISP to run it, I think Hurricane Electric did/does run something like those for free. But in general, yes, it's on the clients to handle.
