Originally posted by Yari
I might be wrong, but this is'nt the case for the "modern" katana.
The problem might be that what we consider a modern katana is just one standard length / curved blade. Katana's havn't always looked this way, see " The Connoisseur's Book of Japanese Swords by Kokan Nagayama".
Why I think that it isn't normal to wear with the blade downward way is that the katana was "invented" to make a faster draw, by letting the curv on the sword be part of the momentum to draw the sword. In doing so you're letting the sword work itself out of the saya. THereby using minimum of force to draw.
If you draw the other way, the sharp side down, you'll always be cutting into your saya. This is the second resaon to why the earth and hevaen cut is so dangerous.
And to arnisador, depending on style, and when you learned Iaido, the draw is made either "sideways" (which is not 100 % true either), or directly with the blad pointing upwards.
/yari