That's absolutely true, but the discussion here centers on home-run style start-ups, which tend to be all or nothing affairs.
One of the reasons for that is that very few start-ups are sustainable in the longer term without acquisition by a larger partner. And if they are they are by definition home-runs, but only very very few (< 1%?) manage to get that far under their own power based on only the initial investment at the time of founding.
And as soon as additional investment is accept the conditions around the company change substantially.
'lifestyle businesses' (which I'm a huge fan of) usually do not require big capital outlays, have a significant chance of staying afloat compared to what is referred to as start-ups on HN and can make more than enough money to make the start-up risk look like it isn't worth it for most players.