South Africa chose to defend the last 4 overs, rather than try and score 16 runs for victory. At first glance this seems like an act of either stupidity or cowardice, but I think it was neither.
They missed out on a chance to make history, by becoming the only team to have successfully chased over 450. But they also missed out on losing a match that would have meant that the series was unwinnable.
Instead Steyn and Philander looked at the options and decided that they were a better team than India, and backed themselves to win the next test. If they went 1-0 down in the series, the best possible outcome was a drawn series, but if the match was a draw, then it was still possible to win the series.
Imran Tahir was probably the next man in. In roughly 2/3 of his innings he has lasted less than 10 balls. That is not the player you want to have saving a test. Morne Morkel is more competent, but it's difficult to bat with only one leg working. It was entirely likely that those two could have been dismissed in the space of an over.
Given that restriction, it made sense that the South Africans decided to be positive with regards to the series, and back themselves to win the second match. It certainly would have been frustrating for them and for any South African fans, but it was probably the correct call.
It appeared to be an act of cowardice, but really it was an act borne of a confidence in their ability to win the second test.