It all comes down to personal preference - as at the end of the day there is nothing 'wrong' in running a twin battery redundancy system on the servos/receiver, just as there is nothing 'wrong' in using an remote optical kill switch to kill your motor over just relying on your throttle servo to be the only source of remotely killing a gas plane's motor (which it can easily be set up to do).
For me, it just comes down to piece of mind when looking at what really comes back to on-board safety systems, which is why I opt to use both a remote optical ignition kill and a backup power supply on my electronics on what is really a rather large and powerful model with a hell of a lot of momentum behind it at full speed (the fact mine is all in one unit is a bonus to me as it reduces unnecessary "links" in the system/chain - which is another bug bare of mine).
And while no single system is ever 100% perfect, I'll happily take a small weight penalty to get mine to where "I" am happy, as I'm more about sport/scale aerobatic flying over 3D where the scale tallies are much more important.