[Swordmaker]

The watch is on a strap that's going to have a permit a varying range of contact depending on how tight the user wears it, and over an area that's not nearly as vascular and might or might not be covered with hair.

No, the plethysmograph on the Apple Watch is what it uses for getting the pulse. It is reading the data clearly enough. Most likely it just has not been FDA cleared for accuracy. There are some reports of calibration problems with differing skin tones. . . but i doubt that is a problem. It is the same plethysmograph that is in the finger tip sensors used in doctor's offices. I think it is just waiting for a software application and FDA approval of the combination. It is not the sensor itself that gets approved but the combination of sensor and software.

[tacticalogic]

It is reading the data clearly enough.

Doing it "clearly enough" doesn't preclude the fingertip meter from doing it better.