$250K/year isn't chump change either. Let alone both having such jobs. Salaries in SV are high but they're not that high for most. At the single income level it's rare to have employees (NOTE: not contractors or business owners) surpass $3-350K.
Plus, if you plan on raising a family[1] then you'd have the added costs of a full time nanny as I doubt anyone with a $250K+ job is going to be around much to raise their kids.
[1]: Which I'm assuming they are if they're buying a 4BR house...
You get promoted once at a place like Google or Apple after 4 years and you're making like 250k/yr (as a software person). 300-350k is easily attainable.
I think there's a lot of people on HN who are unaware of how high comp is at the big 4/5 tech employers.
Plus, if you plan on raising a family[1] then you'd have the added costs of a full time nanny as I doubt anyone with a $250K+ job is going to be around much to raise their kids.
[1]: Which I'm assuming they are if they're buying a 4BR house...