Didn't spend much time in the rest of LA, but I was in westwood for 8 months in 2011. There was less than the tenderloin, but most of the streets with shops had a homeless on every corner. I would walk by 5-10 on my way to grab lunch or dinner.
There is absolutely no comparison between the two places. Even in Westwood Village you could go months without being hit up by a homeless person for change. Now, maybe you were in a hot spot where a few hang out regularly, but they are not everywhere by any stretch of the imagination. They're also nothing like the aggressive homeless population in SF. The police here are very quick to crackdown on any kind of aggressiveness.
If you lived in rural Idaho I could see how you might think Westwood had a lot of homeless people -- anyone from SF would think there were none.