Very good points. Part of why I was able to make the "startup leap" is because my wife and I both worked at Intuit for 7.5 years. We established a good amount of savings that allows us to not have to worry so much about things like the cost of daycare/diapers/etc.
If the finances were tighter, that would add another level of stress to the equation.
I did essentially the same thing before leaving CBS/CNET earlier this year to found http://recent.io/ -- saving salary over multiple years, buying a smaller house on the SF peninsula rather than a bigger one with a larger mortgage, etc. That gave me the luxury of being able to work-full time on creating this recommendation/prediction engine and accompanying app without worrying about income for now.
I guess my assumptions of YC founders are that they are 20-something college dropouts with no previous work experience. Thanks for proving me wrong. This gives me hope that my 25 year old self still has time left :)
In fact, our whole founding team was 30 and married. There are many different configurations for starting a company. My advice is to take whatever your situation is...and use it to your advantage.
If the finances were tighter, that would add another level of stress to the equation.