XC does also, in that every single wallet is a node. Thus, there's no central point that can be targeted for a ddos.
It's the same thing. XC node that participates in anonymization requires an open incoming TCP port, and the attacker can ddos those nodes just as well as drk masternodes.
Very much true in theory, but what would be the point? When you can't see where the transaction is coming from or where it's going, you'd have to choose to attack a random node, and when that node fails to sign off on the funds due to the attack, the funds go on to the next node anyhow.
In addition, transactions are multisig so they require several parties to sign before they are processed. If a bad node alters a transaction to steal funds, or refuses to sign, the transaction won't be processed, so you can't lose funds. Also, since there are redundant connections between nodes that provide multiple pathways for funds, if a node fails to sign a transaction there are others ready to take its place. Pretty cool stuff, really.
The goal when ddos'ing nodes is to first set up many nodes yourself, then ddos the other nodes, so you can then have a control of big enough percentage of the nodes so you can spy the transactions with good enough success.
Again, since transactions are fragmented into small pieces and then sent through the network, this attack would not be effective. The attacker could try to spy the network, but the truth of the matter is that the remaining good nodes are still going to end up handling the transactions, however few they may be. But again, since every single wallet is a node, I just don't see this attack being feasible.