Reed instuments can be ordered with tremelo tuning (reeds tuned to nominally the same note beat) or dry tuning ( the notes are identically tuned so no beat) The Echo harp is tremelo tuned; blues harps aren't (they're single reeds anyway)

Pianos have extra tuning problems, other than Just, Tempered, Pythagorean etc. The low strings produce harmonics that are not an exact multiple of the fundamental (because they aren't a 'perfect' string. This would produce unpleasant beats with higher octaves. To minimise this, the low strings are tuned flat, and the high strings are tuned sharp (stretched tuning).

Stu