It is unclear as to what the initial expectations are, but whatever it is, it is below what was expected. In fact it seems to be actually lower compared to last year’s Galaxy S8, at least that’s what an employee of a local carrier seemed to have suggested. However as it has been pointed out, this is only based on the first day numbers in which a variety of factors could have contributed to the lower figures.
Note that the Galaxy S8 was released later than the Galaxy S9, so it is possible that many customers are still waiting for at least a year before choosing to upgrade. It is also possible that the price tag of the Galaxy S9 and S9+ might be a bit too steep for customers (which was also one of the reasons why the iPhone X isn’t selling as well either).
In any case this is only just for South Korea and who knows, perhaps the Galaxy S9 and S9+ could be well-received in other markets that Samsung operates in. Either way it is too early to tell if the phones are a hit or flop and we’ll probably have to wait a few months for things to normalize.