Yeah but it hardly ever happens does it; I'd love to get 12 solid weeks to show what I can do but I'm stuck trying to build and launch something quite complex in my spare time, it's really difficult so we've taken ourselves to Lanzarote for a full week developing, which we are half way through. You quickly realise that a few issues and a few nights out and your week is over :-/
May not matter if there's cash to make off with. Plenty of folks don't care about long-haul world domination or owning a market; if being a Significant Player for 3 years will earn them enough to retire, why not?
That's fine for you and many others. However, it's an anti-pitch for a YC company: demo day is really auction day. They're selling a chunk of themselves to an institutional investor sifting for disproportionate returns.