Q. Why don't we write G‑d properly?
Often Jewish publications will write G‑d without the "o" instead of spelling the word properly. The Torah (Deuteronomy 12:4) prohibits us from erasing, destroying or desecrating the name of G‑d. G‑d has seven names in Hebrew that are considered holy and forbidden to destroy or erase.
We live in a world that in constantly changing, nothing is permanent. What is "in" today is "out" tomorrow. Only the Creator remains permanent never changing with time and never being effected by things around Him. We celebrate the Creator's stability by ensuring that His written names or anything else that represents Him, is not destroyed.
Because of the prohibition of erasing G‑d's name, we try not to write it in places that it could be erased or thrown out. Over the years we have developed misspellings for all of G‑d's seven Hebrew names. When misspelled, we can erase or throw out what we have written without desecrating a G‑d's real name.
Jewish law generally limits the prohibition of erasing G‑d's name to the Hebrew names of G‑d (His original names). We would therefore be able to erase an English word such as G‑d even if we were to spell it properly. However, there is a view that the prohibition extends to the equivalent of the word G‑d in all languages, that view would prohibit erasing the English word G‑d if it is spelled out properly.
Since it's no big deal to put a dash instead of an "o" and everyone gets what we're trying to say, many Jews and Jewish organizations (such as ours) do it as standard practice in all publications, emails and web posts.