>The last time I looked at the retail quadcopter/RC plane market, when faced with a communications failure most of the quadcopters would return to the launch point and safely land. None of the RC planes had such a function - most seemed to just turn off the propeller and glide in whatever direction they were facing at the time.

Once you have a quadcopter you've got enough digital hardware and software that adding "return to base" is basically free since it's just an additional software routeine.

RC planes don't already have the required hardware/software to implement a return to base feature because they don't need it and of course nobody is going to greatly increase the cost and complexity of the product just to add that one feature.