15 pin SATA connector conflict?

[Billski]

3M's datasheet for its SATA connectors claims the following:  "The power segment is comprised of 15 contacts and is capable of acommodating three different voltage ranges (3.3v, 5v & 12v). Each voltage is allocated three contacts for standard power:  positive(+), negative (-) and ground." It goes on to explain that the other six contacts are grounds, some for hot plugging and staggered pin option.

My question:
I understand that 3 sets of 3 contacts make up 3.3v, 5v and 12v ranges. But the pin set for each voltage range is pitchforked together into one wire, so how can each voltage have a separate positive(+), negative (-) and ground? Can anyone explain? Thanks.

Pin set:
1, 2, 3 = 3.3v (3rd, 3rd, 2nd [2nd is for hot plugging])
4, 5, 6 = grounds (1st, 2nd, 2nd [1st is for hot plugging])
7, 8, 9 = 5v (2nd, 3rd, 3rd [2nd is for hot plugging])
10, 11, 12 - grounds (2nd, 3rd, 3rd [3rd is for staggered pin option] [3rd is for hot plugging])
13, 14, 15 = 12v (2nd, 3rd, 3rd [2nd is for hot plugging)
Note: 1st, 2nd and 3rd references protrusion of pin.