I am not an IP expert. But as I understand it, a Wikipedia page would be copyrighted just like any other intellectual property. However, Wikipedia is a notable opponent of cyberproperty policing. They were very vocal against SOPA when it was proposed in the House. As a result of their philosophy, they explicitly developed a "Creative Commons Deed", available here: http://en.wikipedia.org/wiki/Wikipedia:Text_of_Creative_Commons_Attribution-ShareAlike_3.0_Unported_License. It appears that this would grant you permission to copy and paste an entire Wikipedia page as long as you attribute the source properly.
As I understand it, the DMCA only applies to US-based ISPs and search engines. It's an extrajudicial mechanism that prevents copyright holders from having to litigate every time they want to get rid of a violation. Basically, they notify the host of the "offending" material, and if that entity removes the material or resolves it quickly with the actual alleged violator, the host is insulated from liability. If a copyright holder really wants to block access to content hosted outside of the U.S., they can get an injunction against domestic ISPs to block traffic to the site under the DMCA. I imagine this is rarely done since it's probably a lot more expensive than just sending a takedown notice. The alleged violator can also be sued, but you run into the jurisdictional issues. I don't know if someone running a site accessed in the U.S. is amenable to jurisdiction in the U.S. But the real hammer that copyright holders want to use is the takedown mechanism. They don't want to litigate; it would be like trying to swat flies with a sledgehammer.