Chony,

A balanced cable only does NOT make a connection 'balanced'. A balanced link needs a balanced-output, balanced cable and a balanced-input.
'Balanced' means :
1. signal +
2. signal -
3. ground.

Balanced I/O is more expensive, what will probably be the main reason it it no standard solution.
Especially low-voltage signals (mikes etc.) are sensitive to pickup external (eg radio) signals and in this cases it is very useful to use balanced interfaces because they make it very hard for ext. signals to 'come in'.
(A positive amplitude on the signal+ wire will cause an oposite effect on the signal- wire : total = Zero)

In fact I dislike jacks because they get dirty very easy what causes bad contacts.