I think that the most obviously overestimated thing in this calculation is taxes!!!
By my calculations, a renter family of 3 making 100K, contributing to 401K etc. will pay about 18500 USD in total taxes (Fed+CA+FICA+Med). (Not $25400 as suggested in the post.) That is about 7000 USD difference in take home pay which could influence rent/buy decisions.
Why? Because there is standard deduction, exemptions, child tax credit etc. in the tax code; so you almost need to fill out your tax form to find out how much the tax owed is. I have one excel spreadsheet that I optimized for my situation for this purpose.
Does anyone that fits the above situation, share with us if their taxes are closer to 18K or 25K? I wanted to see if there is any error in my spreadsheet.