I do not find your point about the DLC valid, since when you buy the game, you're paying for what you buy. Not for future releases. DLC should complement the story, which it does. If they brought you to the end of the game, then told you that you had to pay $9.99 for the ending, that would be wrong. You pay for the story that they're selling you, not more.
Your other point about the multiplayer is a valid one. Pirating PS3 games is virtually non-existent, so that cannot be the issue for them. They want to extra money, along with every other developer who is also doing this. We are lucky at the moment that they are not locking down the SP as well, but it looks like everyone will be doing this in the future. This will become an even bigger problem when all games are bought online, such as Apple's app store. We will not be able to share games with family members, etc. To us consumers, it is not "right" for them to do this, but for the company, they can do whatever they want. I agree that I will not buy many games once this happens. What can we do though, other than vote with our wallets?
Edit: For people arguing that buying used games is hurting the industry, it is not. They want you to think that, so don't let them.