For those interested in facts not hearsay take a look at
http://www.sbsa.gov.uk/current_standards/th_html_2006/bsthnd-100.htm.
This states clearly in the intro that insulation is NOT required for
all ground contact floors. For my basement at 2m depth 0.8
perimeter/area ratio, floor value from the table is 0.56 and walls are
0.58 (R=0.5) for no insulation. This is pretty close to what the
u-value calculator said.

Fash