They do have the same number of decimal digits displayed. You can see it by clicking between "float" and "double": the decimal representation stays the same.
It makes it look like they have the same precision (well also, going from 64 to 32 bits zeros out a whole lot, which contributes to that impression). In fact, both decimal representations are usually truncated, and don't accurately represent the binary floating point number. It's a neat and useful tool regardless, and I'm being a bit pedantic.
