Terrorists don't submit to the Geneva Convention - nor do they honor it. Lets not quibble over this - to say the United States is violating the Geneva Conventions and the anti-torture treaties is one thing - but lets not for a second believe that the enemy that the United States is facing right now honors any aspect of the Geneva Conventions.
I would say it is obvious most countries would sign that type of agreement to protect their own troops, I haven't said any different. But I am sure you will agree that this is not the only conflict you will be involved in, so, will your next enemy trust you to hold to the convention? I wouldn't, it's a dangerous precedent to set.

In other words they only sign it so their own troops will be treated humanly if captured. Its like two sides signing a peace treaty and then one breaks it and attacks the other . Now if the otherside strikes back some of you will accuse it of breaking the treaty.
As a country Iraq should be held to the convention and I didn't hear much of Iraqi army units executing their prisoners, there must have been a few prisoners.

As for terrorist units, can they be held to the same standards as a country that thinks it is the leading light in the fight for freedom, I would think that by the very definition of terrorists that they cant. So, should the US or the UK or whoever then fall to their level, I would say if they do then they are the same as the terrorists themselves. You either claim the moral high ground or you don't you can't have it both ways.

Now I've not even said that what has happened in GB is wrong, if it was my choice I would do what was needed to save my countrymen, all I'm saying is that you have made the choice and now you have to live with the consequences.