Why would you marry at all? As you point out yourself, before you succeed it carries a lot of ballast, and increases the risk; and once you're successful, why would one want to tie himself (or herself, for that matter) down?
When you fall in love, you fall in love. Spending time on the relationship at that point is highly worthwhile. And kids are their own reward. Seriously, most of us come hard wired to want kids, and a large portion never realize that until you have your own.
But if you're not ready, then by all means don't get married. But be aware that you're missing out.
Not directed at you, but at the overall thread: honestly, I don't completely get why folks get so revved about others' decisions to get/not get married and have/not have kids. How are your lifestyle choices threatening to my lifestyle choices?
I'd venture that most startup founders experience all of those things. I know I have:)
People who choose not to marry or have kids may be missing out on certain aspects of life, but that does not mean their lives will be any less rich.
Not necessarily true. When you marry (or settle in for the long-term) with the right partner, you help each other develop.
For example my wife and I have very complementary aptitudes. We've helped each other to grow and to become more competent people. Alone, we're pretty good, but together, we're awesome.
If you are lucky, one day you can answer this for yourself.