In my opinion, that's not the issue. It's a matter of respect. For example,
your earthly father might not care if you called him by his first name, but
it's inappropriate to do so. Calling him "Dad" shows proper respect for his
position.
Likewise, G-d might not care what we call Him, but using the dash or "Hashem"
is one way we can show respect for our Creator.
Noah