If this were true, the United Nations wouldn't have included the phrase "...for the purpose of..." after defining the acts that might cons ute torture. They would have just ended with a definition of the acts that cons ute torture.
IF A does Z "...for the purpose of..." Y.
That's intent.
Then, when the United States adds a signing reservation that changes the wording to "...specifically intended..." you change the intent but, whether or not it's torture still depends on an intent.
This is one of the distinction Bybee explored and interpreted to the satisfaction of almost everyone, except you and a few other Bush haters.
Torture isn't just torture, it has specific elements just like any other crime. I'm not going to fault the administration, under the cir stance in which they found themselves on September 11, 2001, for defining the bright line and developing techniques that walk right up to it. I'm satisfied they made a good faith effort to not cross the line while still achieving their immediate goal of obtaining information that ended up thwarting further terrorist attacks and led to the location of Osama bin Laden.
And, according to Bybee (and the convention itself) the UN Convention make a distinction between torture and other cruel, inhuman, or degrading treatments or punishments.
In Bybee's legal opinion, which you're certainly welcome to challenge, he argues the UN only specifically outlaws torture while only discouraging the rest.