A lot of books on Japanese language and/ or culture comment on the fact that there are words which often or almost always take a honorofic prefix o- or go-, even when not speaking politely. They then often say that it is because those things are especially respected or culturally important, but when you look at examples like o-cha (tea) much more than o-shoyu (soy sauce) and o-kashi (sweets) much more than o-sembei (rice crackers), it soon becomes clear that even in the rare cases when that explanation could make sense, there are usually much more convincing candidates for the real reason.
One large group of words are ones where the usual use of the honorific helps make it easier to distinguish from other words which are pronounced basically the same, including o-kashi above. Other pairs include:
o-hashi (chopsticks) but usually hashi (bridge)
o-kane (money) but usually kane (bell)
o-hiya and hiya (cold water and cold sake, always forget which one is which)
This is similar to what I said in my post about the prefix you-.
Others seem to be avoiding one syllable words:
o-yu (hot water)
o-cha (tea – although this is also used to distinguish green tea from koucha, which is black tea)
go-han (cooked rice, or food more generally)
In fact, I can think of very few where it being a particularly respected thing is the best or only explanation. “O-tera” (Shinto shrine) is one example.