My impression is that the results from step II skew in an odd way because there are a lot of test-takers who simply don't care about doing well on it because they did well on step I, took step II later in the year, and only need to pass.
That's why step I is also said by some to be the test that continues to be most reliable... because for step I, you know pretty much everyone is trying to do their best.
However, recently, there's been a trend of thought among applicants that step II is now considered "more important" in some of the competitive fields where everyone is 230+ on step I, removing that pool of would-be non-studyers, and thus raising the average even though the test is still constructed and curved to compensate for a low-scoring group that is no longer as large as it was a few years back... I suspect.
But who thinks about these things? 🙂