The other big difference between LA and SF is like, the penalty for not working close to where you live is absolutely brutal. Taking BART or the subway is moderately annoying, but driving from the Silver Lake to Venice every day is absolutely horrifying.
So in Venice you got Google and Snapchat, although apparently most of Google is getting moved down to Playa Vista, you got a handful of small startups, lots of VR companies led by people with media rather than technical backgrounds (maybe that's fine?), and that's about it.
Nearby you got EA in Playa del Rey (kill me), you got some old companies in Santa Monica and a couple more startups that don't seem interesting necessarily.
Even SpaceX is a pretty far cruise from the Santa Monica/Venice area, but there are a bunch more companies that hire engineers in that El Segundo area, but not necessarily ones that you would want to work at.
It's interesting, certainly, and I think the Snapchat IPO will lead to a lot of rich guys suddenly turning angel and so on. LA has basically never had any real exits until very recently (dollar shave, snapchat), which has limited the development of the ecosystem. Every old guy in LA is like "did you know I founded Myspace?" Based on my time in LA, I would have to estimate the number of founders of Myspace around 3-500. Also stamps dot com.
In summary, I would say LA is pretty much like New York City circa 2005.
The complete secret weapon of LA though is UCLA. The quality of graduates coming out of UCLA computer science is staggering, and from the hiring side, they're not competed for or recruited as heavily as say Stanford kids.