Absolutely NOT the way to think about this. Sure the RDU fluid lasts longer, but fluid does wear out. Considering that the newer MYs can send nearly 100% power (be it momentary) to the back wheels, easy to justify why.
Now, does the PTU need more maintenance. Definitely. It does most of the heavy lifting, being in a FWD-biased system. So you do not have to service the RDU as often as the PTU. But preventive maintenance is good practice, period. RDUs have been known to vent fluid, and grind and whine their way to death. Changing the fluid is easy peasy compared to the PTU. Just do it.