What Maurice told you about Ubisoft's "Uplay Passport" was accurate, but now we have official confirmation and a solid price point to work with. As is becoming the norm, new copies of games will include one-time codes that unlock multiplayer and potentially further bonus content as well.
If you buy an applicable title used and want access to this locked-out content, it's going to cost you $9.99. Ubisoft is launching this initiative "in the coming months," starting with Driver: San Francisco. Expect to see it applied to the company's "popular core games."
Enough publishers are on board with this idea that I don't see it going away anytime soon. Shame you can't buy new games for ten bucks less if you have no intention of playing the multiplayer. That way you're supporting the people responsible for entertaining you and saving yourself a little something on the side.