As far as I know, they just "asked" them not to. Voluntarily. Have they prosecuted or arrested anyone for doing so?
Whether or not somebody has been prosecuted for it is as far as I know unknown as of yet, but a google search will show you many of the news about the military censor of WikiLeaks, amongst which is this.
A memo from the US Marines says this:USMC Personnel (Marines/Civilians/Contractors) are hereby cautioned and directed to NOT access the WIKILEAKS website from a personally owned, publically owned or US Government computer system.
By willingly accessing the WIKILEAKS website for the purpose of viewing the posted classified material - these actions constitute the unauthorized processing, disclosure, viewing, and downloading of classified information onto an UNAUTHORIZED computer system not approved to store classified information. Meaning they have WILLINGLY committed a SECURITY VIOLATION.
Obviously committing a security violation as an employee of the US Marines is, well, not a laughing matter.
Which .com domain have they seized and blocked access to? Sorry if I've missed something here.
You might find more info here.
Yes, governments can, have always, and always will try to control anything and everything and suppress citizen rights. What I am saying is that in the case of Wikileaks, I don't think they have succeeded yet, whereas the statement "censoring websites from the entire world" suggests they have.
In fact I have, as a non-US citizen living outside of the US, have seen one of the results of this censor when trying to access one of the censored sites, getting a warning page with a FBI DVD-like warning. The problem with censoring the domain name itself is that the website can be hosted outside of the US, and yet they'd have power to censor it.