This is a localization (localisation?) issue: different locales have different conventions. It is important to decide on a standard on, say, a project. In the case of an international forum like HN, it makes sense to ask for clarification when necessary. Even if a convention were added to the FAQ, there will always be those who aren't aware of the convention. Cut each other some slack, at least until the HN community decides to launch a satellite.
The thing is, though, the period was in use as a decimal point for hundreds of years, since the time of Napier and Kepler. And then someone in Europe decided to start using commas because, hey, why not, it's cool and fun to be different for no reason.
