The thing is that you want the most common case to be the one that needs no adjusting.
While you'd think that would be the case--and indeed, it
often is--it's not universal. Ease of adjustment has to play a factor as well.
If, for instance, it's
much easier to adjust up than to adjust down (I'm not saying it is, just offering it as an example), then the designers need to strongly consider designing the game to adjust up--
even if that means more people actually have to adjust from baseline.
It's not nearly as obvious a call as you'd think.
And outside of Dark Sun, D&D without a fairly high level of magic items is really, really unusual.
Is it?
That's true if you go by D&D as written. But as played?
Obviously, all I have is anecdote. All any of us has is anecdote. The only people who might--I stress
might--have more are those companies that have gotten comprehensive and widespread feedback. But I know that,
in my personal case, I have played in far more campaigns that differed from the written standard than I have those that followed it. And in every case where a campaign differed, it differed by lowering the amount of magic.
And that, really, is the crux of this whole discussion. "Low magic" and "high magic" mean different things to different players--but the fact is, so does "standard magic."
Far more important than "This is how it's most often been written" is "This is how it's most often been
played." And I don't think any of us have nearly as strong a grasp on that as we think.