Steve rounded portions of numerals don't rest on the base line as flat parts of the numerals. Say for example, a numeral 5 - the flat part on the top of the 5 is bounded by the upper line, but the rounded lower part extends a bit lower than the lower base line. That's why the 2 and the 0 are aligned, but the flat based 2 is somewhat higher than the rounded bottom 0. Put a flat edged ruler along a line of type, and you'll see what I mean.

This usta be my field, only reason I know anything about it.