According to the 2005 Census Bureau estimates …

41.2% of Irvine Households make more than 100K
21.1% make more than 150 K
10.2% make over 200K.

So, the typical median home buyer likely makes between between 100-150K, not 83K. Still overpriced at 600K, but not as out of whack as comparing median household income and median price makes it to be.

http://factfinder.census.gov/servlet/ADPTable?_bm=y&-geo_id=16000US0636770&-qr_name=ACS_2005_EST_G00_DP3&-ds_name=ACS_2005_EST_G00_&-_lang=en&-redoLog=false&-_sse=on
(NOTE: Based on Household Income… the Family income numbers also reported on the link indicate that almost 54% of Irvine families make more than 100K)

FWIW …

30% of Orange County Households make more than 100K.
13.5% make more than 150K
7% make more than 200K