In "real life" there will always be blade on blade contact. Very few swordsmen are so gullible to strike in a way that makes it easy to evade without covering with your sword. Different ryuha tell you to deal with blade contact in different ways. Perhaps that was due to differing methods of sword manufacture used at the time of the school's founding? *shrug* I'm still VERY new to koryu kenjutsu. Having fun with it though.
Anyway, if someone WANTS blade contact to happen (as is done in Kunst des Fechtens) it is all but impossible to avoid it. But so what, since your life is on the line.
Though it seems in many Japanese styles, blade contact is preferred as a deflection. In medieval European styles, blade contact comes from counterstriking/binding as well as deflections, though 90 degree edge to edge contact is avoided in most styles. The preference is edge to flat most of the time.
What it all boils down to is "do what you have to do to kill the other guy". Feces happens, and sometimes your sword will get ruined. It's better than getting your arteries ruined.
Your sword will be damaged in a real encounter, take that as a given. Even if there's no blade to blade contact, the opponent might have protective gear. In medieval Europe, over the course of a sword's life, it will have been repaired and sharpened to the point where the edges were a little wavy, and sometime morphing into another blade type entirely. Even on historical examples that were well cared for, edge damage (although sometimes minor) is often apparent.
Do what your ryu tells you to do. If it says block 90 degrees edge to edge, then do it that way. If it says to use your flat in a hanging parry, then do it that way... they have good reasons for their choices.
Besides, say you were in a sword fight. Assuming you win, you now have TWO swords. Sell one and have the other repaired, or sell both and get a nicer new one.
Best regards,
-Mark