I can relay some of the things Prof. Ng said in the first meeting of the CS229A class:

229A is definitely meant to be much less mathematically rigorous - he said that he expects some people who don't feel like they're necessarily up to 229 to take 229A first to gain more familiarity with the material. From the people that actually showed up to the lecture, it was mostly CS people - although it's hard to say what the online enrollment is like. It is definitely meant to be useful to anyone who wants to be able to get machine learning algorithms to work, not necessarily understand their finer points.