Exactly. But even if you don't indulge in such schemes, including a transaction in your block at high volumes will cost you (high) personal expenses, while the beneficiary will be general public. Some people will inevitably cheat in these conditions, trying to parasite on the rest of the network. It will inevitably lead us to the Tragedy of the Commons problem.
A cryptocurrency architecture that relies on altruism while cheating can be beneficial to some extent, is far inferior to an architecture, where no egoistic behavior can ever gain you any benefit. I would not bet any significant fortune on the PPC because of this reason unless this aspect is fixed, and so would many other investors probably. Therefore I see not future for the PPC so far...
It is no altruism not to cheat. The benefit of not cheating is keeping the value of the coins. You can for sure try to undermine Peercoin (as you can undermine every single crypto coin) this way. But undermining it to gain profit doesn't work this way. You ruin the trust and hence the value if you act like this. There is no benefit in excluding transactions from the block chain. The architecture doesn't rely on altruism but on maintaining the value of the coin!