Why does Phantom Dancer keep track of how many times it saves your life, but Death's Dance doesn't?

PD just reduces damage, it's not anything fancy. Not like Death's Dance, which delays it so you have a chance to lifesteal up to save yourself. Keeping track of how many times PD saved you is no more meaningful than keeping track of how often a cloth armor has saved you, but tracking DD actually shows something notable. Hell, even the counter is called "Deaths Defied", which sounds like it belongs on Death's Dance.