Madcow does it that way because he's experienced enough to know *why* he's doing it that way. The single resistor method saves space, and gives a baseline level of resistance to keep your LEDs from overdrawing current and doing Bad Things (tm). If you're doing color mixing, you'll still need a second resistor for at least one of the LED dice, so you're not really saving any effort on wiring.

There's no real difference to hooking up a standard resistor on the (+) or (-) side. My only recommendation is to choose one or the other, and then be consistent. The DynaOhm resistor is an exception to this rule, and it MUST go on the (+) side of the LED, and polarity is important on it.