Detention?
Why is it that people seem to be referring to Assange's current situation as detention? He's not detained. He is avoiding detention by choice. His current situation is that he chose to live in a Knightsbridge flat, a prime location, with guards and concierge service, and even allowed to have a pet. He is free to go - at the risk of actually being detained to finally answer to some allegations.
The US don't want him. He has made himself quite irrelevant already (apart from some mediocre entertainment value). If they wanted him, they would have done so long before he managed to break his bail conditions. He's not a British Citizen, so the UK wouldn't have hesitated to hand him over, if asked nicely.
Biting the hand that feeds IT
