Now think of a contracts protocol that's much more complex than Bitcoin's. Those contracts have their own "confirmation" rules which are governed by the "meta" protocol that's managed off the Bitcoin blockchain. Although the bitcoin blockchain can act as the "transport" mechanism for those contracts, it can't actually validate them because it doesn't understand the contract protocol.
Furthermore, a new Bitcoin block containing a contracts transaction is NOT a "hash" of all the contract confirmations that went before it - that still has to be done by the meta protocol which then has to potentially thread it's way back through the whole ancestry of transaction history for that particular contract, effectively requiring it to scan the whole Bitcoin blockchain just to confirm.
FUNCTIONALITY - HOW PROPRIETARY BLOCKCHAINS WORK
On the other hand, when these Bitcoin 2.0 protocols use proprietary blockchains, the blockchain *can* behave in a manner more analogous to bitcoin because they inherit the contracts protocol for the purpose of verification. That's why the approach that NxT, Etherium etc have taken will always blow the Bitcoin metacoin approach out of the water for speed, functionality, user experience.
I guess I don't understand how clearinghouse makes use of SPV, if it is required for clearinghouse to work or just makes the clients run faster. Does anybody know some source material to help gain a better technical understanding of clearinghouse? Any good posts providing a good counter-argument to Vitalik's opinion on the matter of SPV?
TIA
Edit: found some discussion on counterparty forums. Guess I had it backwards, Vitalik's argument is that clearinghouse et. al. do not inherit SPV so have to scan back to the beginning of the blockchain to verify transactions as valid, making the process slow and unscalable.
https://forums.counterparty.io/discussion/214/vitalik-s-debate