Just looking at the Wu-Decimal page, though, I can't tell whether they're internally exact rationals or base-10 floats. If they're base-10 floats, they have all the same issues base-2 floats have. If they're internally exact rationals, I wonder what they do for division, which the set D isn't closed under.
My favorite representation so far pairs a signed float in [2^-512,2^512) with a signed integer to extend the exponent range. The idea is to avoid overflow and underflow, particularly when multiplying thousands of probabilities.
(On average, adding a few thousand log probabilities or densities and then exponentiating the sum yields a number with about 9 digits precision. Worst case for adding log probabilities and exponentiating is about 8 digits precision, and for adding log densities it's 0 digits. Multiplying the same number of probabilities or densities retains about 13 digits in the worst case.)
Nitpick: although base 10 floats have similar issues related to being of limited precision, they are superior to base 2 floats in the aspect of representing decimal numbers without the binary approximation: e.g. 1/10 is nonrepeating as 1.0 x 10^-1 but infinitely repeating as binary, so for IEEE 754 binary32 you get 1.10011001100110011001101 (1.60000002384185791015625) x 2^-4.