This can also be something of a trap. For some time now I have worked as a housecleaner and there is a common scenario that I have learned to avoid: Clients are friendly and ask how you are. Cleaners then answer honestly about how this is an opportunity for them and hard physical work is all between them and crushing poverty. Clients are generally unprepared for the extreme problems that people living as cleaners may…
This is not unique to interactions between the well off and not well off. It's true that in most case, when people ask "how are you", they're not looking for a detailed answer. It's a pleasantry, and the expected answer are of a more general form ("ok", "great", "not great, but getting by", "not a great day", etc).
As a side note, I have a cleaning lady and have gone through a number of them over the years. Some of them we've been friendly with (we knew the names of her kids and asked about them, etc), some we were only passing acquainted with (friendly, but in the general way above). It can vary a lot depending on the people involved.