I know a fairly diverse range of people and have lived an several places where there has been an even mix of social and cultural backgrounds - both rural and urban.
I was just reading a diet/science thread from a few months ago and there is a lot of discussion surround poverty and obesity (which I am certain is true), except many people classified 'poverty' and 'working class'.
I think this is a really odd presumption. I have met many poor MC and well off WC and it has been unpredictable to say the least. The main difference between these groups have mostly been in their tastes, beliefs, interests, and behaviours, not cash flow.
The poorest people I have witnessed were possibly originally in one of the above social groups, but to presume poverty is synonymous with being working class is problematic.
I suppose if one has only ever existed in a very wealthy environment then the presumption may seem genuine, but I'm quite certain it is not. I would personally say that I have observed that different social groups respond differently to poverty, hence creating these stereotypes. Typical WC jobs tend to pay less, that is for certain, but it still seems odd to associate poverty with a group that regularly earns and owns property.
Is there an extra group which fits the definition better? I don't know. What I do know is that noting is simple - I grew up MC, the environment, the education, but have rented all of my life through choice (I am an artist and like to move around), so some may presume, on paper, I am something other than what I am, until they meet me and chat!
I would conclude that much of this lies with education, and I don't just mean academically. Cultural and social capital, and having learned how to react in a crisis, both in the home and later, at school. Many don't have that privilege and never learn how.