messagenews: snipped-for-privacy@k35g2000prh.googlegroups.com...
Yes, it's a ridiculously tight spec. Their "object" is likely going to be bigger than that. 10cm is not out of the bounds of professional surveying GPS units, but they are not cheap.
I assume the OP is US based so that means WAAS access which improves things. With averaging and a good antenna you should be able to get sub 1m repeatability with a