There are several reasons why a design can design the use of multiple pins. In order of importance:
Connecting two pins in parallel lowers the resistance of the pin connection - a designer might consider low impedance important to avoid interference on the power supply lines
There is a limit to the current allowable through a single pin.
If power is extremely critical, a designer might decide to parallel two pins to lower the probability of contact problems (improve reliability).
Finally, if the host board has already 2 pins wired to each Vcc and Gnd, why not use them?
Note that the single pin board is for soldering. There you take the responsability. If you use a wired connection, you won't have problems.
And your remark on CPUs having many pins for each, is not correct. In CPUs the multiple pins are really to lower the resistance to the power supply. If they'd use only one pin, the socket would probably burn, because of the heat generated in the contact. Also, with a CPU, the power filtering capacitor is on the board, so it is vital that the impedance from the chip to the capacitors is very low.