You're right, Leeneia, a lot of published songs are too high for most voices. In church music, including carols, the tune is often pitched for sopranos or boy-trebles, with the other parts underneath. When the general congregation attempt to join in, they are (understandably) attempting to sing the tune, and that's why many of them find it too high. I reckon that puts a lot of people off singing - they find the range uncomfortable or impossible, and they think, "Well that proves it, I can't sing".

I'm not sure how "midwest American" voices fit into this, but I think it's true that taller people tend to have lower voices. This may be why the Italians, Irish and Welsh produce so many good tenors - they're not the tallest of races. In many countries, people are now taller than their parents and grandparents were, so the average pitch may well be somewhat lower than it used to be. Another factor is that the voice tends to drop a bit as you get older.

When it comes to choosing a key, there can't be any one key that works best even for one singer, as it all depends on the range of a particular song. It's a matter (as others have said) of considering the range of the song, knowing the singer's comfortable range, and finding the key that brings these together.

Marje