As the OP pointed out, almost everyone leaves out the entire name of the statistic they quote when they site a “median income” of $89,872 for Nassau County number. Again, that number is actually the statistic of median HOUSEHOLD income. This is the cumulative income of everyone over 15 years old in that household. For many households that includes multiple individuals and/or those with multiple jobs. This is not the statistic of what the median salary is in Nassau County. Tried to find another source for this but it is a little hard to find - although this site
Powered by Google Docs has a figure of $46K across all industries for 2005, so the $49K figure may not be that far off.
Not following the general rule of spending no more than 3X the borrower's annual income is one of things that got the housing market in the trouble it is in now.