Here's Greyhawk's take on the issue.
My reaction? Well, I don't know. I don't trust NPR much to begin with, and when they say things like, "Critics say it's an attempt to suppress unflattering truths about the U.S. occupation" when Mil-Blogs are actually one of the ways you can bypass negative media accounts to actually hear good news about the continuing liberation* in Iraq.
I can understand the need for Operational Security. Our enemies say they can get 80% of what they need from open sources. We are accustomed to openness, and I can see the need to remind people to be careful what information they give out...even if it comes in the form of a warning that some people feel is somewhat threatening.
I also suspect that 'bandwidth' might be an issue. You don't want to miss an important message because someone is uploading an image to their website.
I can see a reason why some higher ranking officers might want to discourage blogging without actually saying "no". The less people doing it, the less chance there is of problems, but the people who really find it useful and soul-satisfying aren't barred.
To tell the truth, I am far more disturbed that the USAF (and maybe the rest of the military, dunno), totally blocks access to the portal mail servers (Yahoo, Hotmail, AOL). Even worse, they don't warn you before you deploy. It can be a significant morale hit to not be able to receive email or even be able to tell someone you won't be able to read their email until you return...
*I never liked 'occupation'. I know President Bush used it at least once, but we didn't occupy a nation being governed willingly, we freed a people from a tyrant. The tyrants supporters and allies are still resisting our attempt to guarantee that the people remain free. Not every citizen wants us there, but the local people with perspective on the situation recognize the necessity. Describing that as an 'occupation' is clumsy at best and reprehensibly manipulative at worst.