Not as such, it's just that v4 is so small that most ISPs don't bother to give routed prefixes -- or rather they can't, since there aren't enough addresses avai

Not as such, it's just that v4 is so small that most ISPs don't bother to give routed prefixes -- or rather they can't, since there aren't enough addresses available to do so. In v6 it's typical to get something like a /56 from your ISP, which is 2^(128-56) = 2^72 addresses. (v6 also has a protocol, DHCPv6-PD, to manage prefix delegations automatically, whereas v4 requires manual config or some custom mechanism.) You could argue that the difference between 2^32 and 2^128 is big enough to be considered a fundamental difference. (Also: "lets".)