"Without seeking exemption from the law" is the key phrase. He refused to respect a discriminatory law, and, by living there, was effectively daring the Apartheid government to arrest a sitting archbishop.

1) why would a US president want to live in the White house in DC? It doesn't matter what they want, the official residence comes with the job. I do not think that Mr Tutu spent every single day of his tenure in Bishopscourt - you are right, it wasn't his scene. But he was a common sight there.

2) It was literally illegal for Mr Tutu to live there, then. Doing so anyway, with the backing of a major church, who chose to send him there, was a political act. Which he performed with good humour.