There's a legitimate rant to be had about using elephant architecture to serve mouse traffic, and I think that's what annoys me most about the NoSQL fad. But that doesn't mean the problems mentioned in this article don't exist.
I'm not sure I understand. If I make an application that has to increment a counter, shouldn't I always be worried about concurrency?
What I mean is, sure, if I'm serving only a few requests, then of course the probability of running into concurrency issues is lower than a site with more requests/sec. But it's still a matter of chance, there is some probability that two requests will come in at exactly the same time and cause a problem.
The parent poster is worrying about performance of concurrency. This doesn't need to be worried about unless you are one of about 5-10 tech companies whose name is recognisable to people on the street.