What is the incentive for both PoS and PoW miners to build on top of PoW blocks?

From the Peercoin whitepaper:

The block chain with highest total consumed coin age is chosen as main chain.

And it has been said in this forum that PoW blocks don’t contribute to secure the network, which is consistent with the quote above. Suppose this: the latest block of the longest chain per coin age consumed ends with a PoW block, like this:

[tt]First block ever<-…<-Pos<-PoS<-Pow[/tt]

What incentives do all miners (both PoS and PoW) have to build the chain on top of the latest PoW block of that chain instead of skipping it (and all other PoW blocks up to the latest PoS block)?.

Most Peercoin users will behave honestly, and so they will mine on top of the latest PoW block in the above case, but if somebody paid for already received goods or services and that transaction has been included in the latest PoW block, then he has an incentive to mine on top of the latest PoS block in order to revert the transaction, or in other words, double-spend his peercoins. From what I get, if the attacker is successful in finding a PoS block skipping the latest PoW block, the network would accept his block, discarding the PoW works that contained his transaction, and therefore the attack succeeds, and he has nothing to lose other than doing harm to the network in which he holds money (that applies to any attack).

What (if anything) prevents this attack scheme?. I think that this is different from the mining in all chain forks attack described commonly by “nothing-at-stake”.

Thanks in advance.

The attack does not sharply increase the risk of a double-spend, since most blocks are PoS staked, not PoW mined. Two successive blocks are very unlikely to be both reversed. However, I think this is a valid attack that hurts PoW miners by excluding their reward.

Good thinking!

This attack has been discussed on these forums. See this thread: PoS miners can rule over PoW miners.