In Voyager, the situation is admittedly different, but they talk specifically about replicator credits. It could be that there's a de facto currency depending on the environment one's in. Alternatively, they could be common sayings that have outlived their literal meanings (becoming something akin to idioms) or, if you prefer some meta, they're translations of what the characters actually say into the parlance a 20th-/21st-century audience is more comfortable with.