In theory, you're right, but in practice that's so, so not the case, especially here in the SF Bay Area, which seems to be neck-deep in the "build-first" mentality of freshly minted MBAs.
Over the last year I've talked with so many startups, mostly "founders" and "entrepreneurs" with Bschool degrees, who seem to be taught that all they need is an "idea/vision". They just need to get someone to build it, because, you know, they've run the numbers and they "know the market" (actual, real-life quote from an actual situation). When I ask, "What problem does this solve, for whom, and how do you know this?", they scoff and tell me that they don't need to do any user research and besides, that'd slow things down.
Now, there may be actual pressures on startups to start building without ever observing a single potential user. Certainly if you're going to present at Y Combinator, they want to see code, a product, and tons of "confidence" (again, actual quote from actual situation). Showing them serious research on populations, data on engagement, prototypes... that'll get you laughed out.
But, side note: 75 to 90% of all startups fail. Go figure.
As a UX professional, this really grinds my bacon, six ways to Sunday. It's like seeing a kid whinge that the test was hard when you know they didn't do any of the homework. Perhaps they think that user research means months, and 100s of pages of specs (and, to be fair, it could), but I think a lot of this comes not just from stakeholder pressure but a misreading or Ries's "Lean Startup". Sure, it helps to get something in users' hands quickly, but this is based on research first. Know who your users are, what problems they face, how they think. At least an idea of it. You can rapidly prototype, GOOB, test, iterate, all within cycles of days or weeks. But you HAVE TO KNOW THE USER (who is NOT YOU) first.
There's a great example of how this can be done for $40, to save $10Million: http://vimeo.com/24749599