This is indeed a new feature (introduced in September 2011) to prevent abuse of the bounty system.This is mentioned explicitly in a few meta answers but, as far as I can tell, not in FAQs.
One way this abuse was done was:
Someone would post an answer on someone else's question, and then place a bounty on the question to draw attention to it. He would then gain more upvotes from the publicity than he spent on the bounty. The spend was raised to 100 to discourage this.
The reason it applies even if your answer is deleted, is because you might still undelete the answer.
