Here's what I think:
1. Most people bought before the unprecedented price run-ups of the past 10 years or so; thus while OC has always demanded a premium compared to many other parts of the country, there was some relationship to basic economic fundamentals. ie: price to income ratios made at least some sense way back in the 90's.
2. In more recent years many others were able to buy up after their $350,000 homes suddenly became $800,000 homes in a matter of just a few years. You don't necessarily need the big income if you have a huge chunk of change to use as a down payment.
3. There are more areas in OC than you may think where starter homes vacated by the move-up buyers mentioned above are purchased not by nuclear families, but by much larger extended family groups.
Also I just read about one program, sponsored by a RE group, where 1st time home buyers making under $90,000 a year can qualify for grants of up to $15,000 to use toward their downpayment.
Both help keep prices up and the whole process going.
4. When prices were spiraling up and up and up it was easy for folks to get caught up in the buying frenzy. ie: you've got to get in while you can and by using any means necessary... it was no big deal for folks to buy waaay more house than they could legitimately afford since in a matter of months they would have instant equity just due to price increases.
OC has been a hot bed for creative financing in recent years.
5. Yes, there are lots of folks with big bucks in OC, so not everyone has to be in debt up to their eyeballs just to get into a house in OC.
That said, IMO those with incomes of $200,000+ a year are still in the minority, even in OC, so the multitude of million+ dollar middle class tract homes makes no sense.
