You don't see many dumb people at small companies, mainly because there is no place to hide. In a small company you need to carry your own weight, and if you don't it is pretty obvious. In a large company it isn't as obvious to find the slacker.
I'm going to assume the author just doesn't have enough experience to realize just how naive this is. Startups employ dummies all the time, and you can't tell because everyone is too busy to pay attention, they're good at playing politics, they're friends with one of the founders, or they are one of the founders. And yes, sometimes these startups are successful in spite of that one or two idiots.
Working for a big company has a different feel to it, and you normally have to worry about office politics and other things that you don't have to worry about in a small company.
Well, if "small" is two people or less, this is correct. But politics comes into play whenever you have 3 or more people. Granted, the politics may be easier to understand and manage, but they're much more ugly than in a big company.
In short, it sounds like the author found a good startup to work for, which is usually better than most BigCos. But it's all downhill from there. If the author stays in the startup game for long enough, I guarantee he'll work for a company that will make him miss BigCos and their rules (some of which benefit the employee).