The manufacturers stopped selling the complete sets due to three simple facts:
1) Most of the aircraft being sold today are either ARFs or kits that are more complex than in the past. This means that many of the ARFs either already have radio gear or at least have the servos already installed. As for kits, most builders prefer certain types of servos for certain applications so they end up either buying servos after the fact or they have what they want on hand so the low cost servos supplied are a waste of money for both seller and buyer.
2) The manufacturer can sell the required battery packs and servos at a higher profit margin than what they would have gotten if sold as part of a complete set.
3) Battery tech is evolving faster than the radio manufacturers can adapt. By including a removable dry cell tray, the buyer can either use the radio as purchased or install whatever they want for power packs. For example, when I bought my Futaba 4PLS surface radio, it came with a matched receiver and dry cell tray but with the programming to use dry cells, nicad/nim AND LiFe packs. All you had to do is set the transmitter to the type of power source used so the warning features would work properly