One of the items from snopes.com
Dirt poor is an American expression, not a British one. Claims that the
saying grew out of British class distinctions as measured by style of
flooring are therefore just plain silly.
As mentioned briefly above in the "everybody slept on the floor"
discussion, floors were never bare dirt anyway. Fresh reeds were laid on
them every day and thrown out every night, with another fresh set
brought in for sleeping on. In the summer months, aromatic herbs might
be added to this vegetive underfooting.
This reminded me of a wonderful passage from Pope:
In the worst inn's worst room, with mat half-hung,
The floors of plaister, and the walls of dung,
On once a flock-bed, but repair'd with straw,
With tape-ty'd curtains, never meant to draw,
The George and Garter dangling from that bed
Where tawdry yellow strove with dirty red,
Great Villiers lies . . . .
_Epistle to Bathurst_, 299-305.
The T.E. editor quotes Aldous Huxley on the lines: "I remember I the
first time I read Pope's lines, being profoundly impressed by those
walls of dung. Indeed, they still disturb my imagination. They express,
for me, the Essential Horror. A floor of dung would have seemed almost
normal, acceptable. But _walls_--Ah, no, no!"