My first thought was than any employer has the right to limit what sort of sites its employees can access with company resources and/or company time. I realize that the US Army isn't your everyday employer, but when I look at it in those simplest of terms, it makes sense to me.
And yeah, a lot of the same information can trickle out via email, but even if you have a huge forward list, it's not like the information is going to be disseminated like it would if it were on a public web page.
"How do you like THAT 'misanthropic panache,' Mr. Goldstone?" - PalJoey