This hasn't been my experience in general. Most of my hard interviews were at startups. To sound old and jaded, I think a lot of it has to do with the startup mentality "we only hire the top 0.0001% of coders " . Once you've been in the business for years you realize the fallacy of that thinking and try to hire good coders with a focus on finding people fun to work with.
Most big companies I applied at had about half of the grilling and the rest of the interview was "culture fit"
I'm a bit jaded about startups myself and I'm not even 30. The couple I worked in seemed like "we are so smart" cults, which drove me absolutely nuts. The people working there were smart, but their definition of intelligence was narrow-minded. I find it very unlikely that you are hiring the "best-of-the-best" if the vast majority of your employees are men under the age of thirty who attended a very specific list of colleges.
Running a company is a team activity. I think there are too many sports metaphors in business, but if you've ever played a team sport you realize that the best teams are usually the ones with the players who play best together, not the ones with the most talented players. I could run this metaphor in to the ground, but the point is that hiring only the "best-of-the-best" is neither a credible claim nor a good methodology for creating a successful business. You might be able to do that when your company is 5 people, but it's probably much better to have good role players who are a cultural fit for your organization in the long run.
Most big companies I applied at had about half of the grilling and the rest of the interview was "culture fit"